All 400 quiz questions in 10 units, with the correct answer and an explanation for each. Read a unit, then test yourself in the Senior 3 quiz.
1.What is the shape of the path (trajectory) followed by an object in circular motion?
Answer: A
By definition, circular motion means the object's trajectory is a circle of fixed radius.
2.Angular displacement is measured in which unit?
Answer: D
Angular displacement (θ) is the angle swept and is measured in radians (rad).
3.How many radians correspond to one full revolution (360°)?
Answer: C
One complete revolution corresponds to 360°, which equals 2π radians.
4.Convert 180° to radians.
Answer: A
180° = π radians, since 360° = 2π rad, so 180° = 2π/2 = π rad.
5.Which formula correctly defines angular velocity ω?
Answer: B
Angular velocity is the rate of change of angular displacement with time, ω = Δθ/Δt.
6.What is the SI unit of angular velocity?
Answer: C
Angular velocity has units of radians per second (rad/s).
7.The period (T) of circular motion is best described as:
Answer: D
Period T is the time required for one complete revolution around the circle.
8.Frequency (f) of circular motion is defined as:
Answer: D
Frequency is the number of complete revolutions per second, measured in hertz (Hz).
9.Which equation correctly relates period T and frequency f?
Answer: C
Period and frequency are reciprocals of each other: T = 1/f.
10.An object moves in a circle of radius 0.5 m with angular velocity 4 rad/s. Find its linear speed v.
Answer: B
Using v = ωr = 4 × 0.5 = 2 m/s.
11.An object completes one revolution of a circle of radius 2 m in 4 s. What is its linear speed?
Answer: A
Circumference = 2πr = 2π(2) = 12.57 m; v = distance/time = 12.57/4 ≈ 3.14 m/s.
12.In circular motion, the centripetal force always acts:
Answer: B
Centripetal force is directed radially inward, toward the centre of the circular path.
13.Which formula correctly gives the centripetal force?
Answer: D
The centripetal force is Fc = mv²/r (equivalently Fc = mω²r).
14.A 2 kg object moves in a circle of radius 1.5 m at 3 m/s. Calculate the centripetal force.
Answer: D
Fc = mv²/r = 2 × 3²/1.5 = 2 × 9/1.5 = 12 N.
15.A 0.5 kg mass moves with angular velocity 2 rad/s in a circle of radius 2 m. Find the centripetal force using Fc = mω²r.
Answer: A
Fc = mω²r = 0.5 × 2² × 2 = 0.5 × 4 × 2 = 4 N.
16.Centrifugal force is best described as:
Answer: D
Centrifugal force is not a real force; it is an apparent outward force experienced by an observer in a rotating (non-inertial) frame of reference.
17.What provides the centripetal force needed for a car to move around a curved road?
Answer: A
Frictional force between the tyres and the road surface supplies the centripetal force for cornering.
18.What provides the centripetal force that keeps a satellite in orbit around the Earth?
Answer: B
The Earth's gravitational pull on the satellite acts as the centripetal force keeping it in orbit.
19.If the centripetal force on an object moving in a circle suddenly disappears, the object will:
Answer: C
By Newton's first law, without a centripetal force the object continues in a straight line tangent to its circular path at that instant.
20.Why are roads banked (tilted) on sharp curves?
Answer: C
Banking provides a component of the normal force toward the centre, reducing dependence on friction for the centripetal force.
21.If the radius of a circular path increases while speed stays constant, the centripetal force:
Answer: B
Since Fc = mv²/r, for constant m and v, Fc is inversely proportional to r, so a larger r means a smaller Fc.
22.If the speed of an object in circular motion is doubled while radius and mass stay constant, the centripetal force becomes:
Answer: B
Since Fc ∝ v², doubling v increases Fc by a factor of 2² = 4.
23.The second hand of a clock takes 60 s to complete one revolution. What is its angular velocity?
Answer: C
ω = 2π/T = 2π/60 ≈ 0.105 rad/s.
24.The minute hand of a clock completes one revolution in 3600 s. What is its angular velocity?
Answer: A
ω = 2π/T = 2π/3600 ≈ 0.00175 rad/s.
25.Approximately how long does the Earth take to complete one rotation about its own axis?
Answer: A
The Earth rotates once on its axis in about 24 hours (one day).
26.A geostationary satellite has an orbital period of approximately:
Answer: D
A geostationary satellite orbits with a period equal to Earth's rotation period, about 24 hours, so it stays above the same point on Earth.
27.In uniform circular motion, which quantity remains constant?
Answer: C
In uniform circular motion the speed (magnitude of velocity) is constant, but the direction of velocity continuously changes.
28.At any instant, the velocity of an object in circular motion points:
Answer: B
The instantaneous velocity is always directed tangentially to the circle at the object's position.
29.In uniform circular motion, the acceleration of the object is directed:
Answer: A
The centripetal acceleration always points toward the centre of the circular path, causing the change in direction of velocity.
30.A wheel makes 300 revolutions in 60 seconds. What is its period of rotation?
Answer: B
f = 300/60 = 5 Hz, so T = 1/f = 1/5 = 0.2 s.
31.In uniform circular motion, the speed of the object remains constant.
Answer: True
Uniform circular motion is defined by constant speed, even though velocity direction and acceleration change.
32.In uniform circular motion, the velocity vector of the object is constant.
Answer: False
Although speed is constant, the direction of velocity continuously changes, so the velocity vector is not constant.
33.Centripetal force acts away from the centre of the circular path.
Answer: False
Centripetal force always acts toward the centre of the circle, not away from it.
34.Centrifugal force is a real force acting on an object observed from a stationary (inertial) frame of reference.
Answer: False
Centrifugal force is a fictitious (apparent) force that only appears to act in a rotating, non-inertial frame of reference.
35.The period T of circular motion is inversely proportional to the frequency f.
Answer: True
Since T = 1/f, period and frequency are inversely related.
36.The SI unit of angular velocity is ______.
Answer: rad/s (radian per second)
Angular velocity is expressed in radians per second because it measures angle swept per unit time.
37.The force that keeps an object moving along a circular path, directed toward the centre, is called the ______ force.
Answer: centripetal
This inward-directed force is necessary to continuously change the direction of the object's velocity.
38.One complete revolution corresponds to an angle of ______ radians.
Answer: 2π
A full circle subtends an angle of 2π radians (360°) at the centre.
39.The time taken for an object to complete one full revolution around a circle is called the ______.
Answer: period
The period (T) is measured in seconds and represents the duration of one complete cycle.
40.In circular motion, the velocity vector at any point is always directed ______ to the circle.
Answer: tangent(ially)
The instantaneous velocity is tangential because it represents the direction of motion at that point on the circle.
1.Which formula correctly defines linear momentum?
Answer: B
Linear momentum is the product of an object's mass and velocity: p = mv.
2.What is the SI unit of linear momentum?
Answer: D
Momentum has units of mass × velocity, giving kg·m/s (equivalent to N·s).
3.Calculate the momentum of a 4 kg object moving at 5 m/s.
Answer: C
p = mv = 4 × 5 = 20 kg·m/s.
4.Which formula correctly defines impulse?
Answer: A
Impulse is the product of force and the time interval over which it acts: J = FΔt.
5.Impulse delivered to an object is equal to its:
Answer: C
By the impulse-momentum theorem, J = FΔt = Δp, so impulse equals the change in momentum.
6.What is the SI unit of impulse?
Answer: C
Impulse can be expressed in newton-seconds (N·s), which is dimensionally equal to kg·m/s.
7.A force of 50 N acts on an object for 0.2 s. What is the impulse delivered?
Answer: B
J = FΔt = 50 × 0.2 = 10 N·s.
8.An object's momentum changes from 10 kg·m/s to 30 kg·m/s in 2 s. What is the average force acting on it?
Answer: A
Δp = 30 − 10 = 20 kg·m/s; F = Δp/Δt = 20/2 = 10 N.
9.The law of conservation of linear momentum applies to:
Answer: D
Total momentum is conserved only when the net external force on the system is zero (an isolated/closed system).
10.Which best describes an elastic collision?
Answer: B
In a perfectly elastic collision, both momentum and total kinetic energy are conserved, and the objects move apart afterward.
11.Which best describes a perfectly inelastic collision?
Answer: D
In a perfectly inelastic collision, the objects stick together after impact; momentum is conserved but kinetic energy is not.
12.A 2 kg trolley moving at 5 m/s collides and sticks to a stationary 3 kg trolley. Find their common velocity after collision.
Answer: C
Using conservation of momentum: (2×5 + 3×0) = (2+3)v → 10 = 5v → v = 2 m/s.
13.A moving ball collides elastically head-on with an identical stationary ball. What happens?
Answer: C
For an elastic head-on collision between equal masses, the velocities are exchanged: the incoming ball stops and the target ball moves with the initial velocity.
14.How do airbags in cars help reduce injury during a collision?
Answer: D
Airbags extend the time (Δt) over which the passenger's momentum changes, which reduces the force (F = Δp/Δt) exerted on the body.
15.How do seat belts help protect passengers in a crash?
Answer: C
Seat belts stretch slightly and restrain the body over a longer time, decreasing the force needed to stop the passenger's momentum.
16.Rocket propulsion works mainly on the principle of:
Answer: C
As gases are expelled backward with momentum, an equal and opposite momentum is given to the rocket, propelling it forward, in line with conservation of momentum.
17.Why does a gun recoil when fired?
Answer: A
Since total momentum before firing is zero, the gun must move backward with momentum equal in magnitude but opposite in direction to the bullet's forward momentum.
18.A 0.02 kg bullet is fired at 400 m/s from a 4 kg gun. Find the recoil speed of the gun.
Answer: A
Momentum conservation: 0.02 × 400 = 4 × v → v = 8/4 = 2 m/s.
19.In an isolated system, the total momentum before a collision compared to after the collision is:
Answer: A
For an isolated system with no external forces, total momentum before equals total momentum after the collision.
20.Which of the following is a vector quantity?
Answer: D
Momentum has both magnitude and direction (p = mv, and velocity is a vector), so it is a vector quantity.
21.A 3 kg cart moving right at 4 m/s collides and sticks to a 2 kg cart moving left at 3 m/s. Taking rightward as positive, find their common velocity after collision.
Answer: D
Total momentum = 3(4) + 2(−3) = 12 − 6 = 6 kg·m/s. Combined mass = 5 kg. v = 6/5 = 1.2 m/s (to the right).
22.Newton's second law, expressed in terms of momentum, states that force equals:
Answer: A
Newton's second law can be written as F = Δp/Δt, the rate of change of momentum.
23.A heavy truck and a light car travel at the same speed. Which has the greater momentum?
Answer: B
Since p = mv and both have the same v, the truck's larger mass gives it greater momentum.
24.Why does a boxer 'ride the punch' by moving their head back when hit?
Answer: B
Moving back extends the time over which the momentum changes, lowering the average force (since F = Δp/Δt) and reducing injury.
25.A stationary object of mass 10 kg explodes into two fragments. What is the total momentum of the fragments immediately after the explosion?
Answer: B
Since the object was initially at rest, total initial momentum was zero; by conservation, the fragments' momenta must sum to zero (equal and opposite).
26.A 10 kg object at rest explodes into two pieces: a 4 kg piece moving at 9 m/s and a 6 kg piece. Find the speed of the 6 kg piece.
Answer: D
By conservation of momentum, 4 × 9 = 6 × v → v = 36/6 = 6 m/s, moving in the opposite direction to the 4 kg piece.
27.Which type of collision conserves total kinetic energy?
Answer: A
Only elastic collisions conserve both momentum and total kinetic energy.
28.Which type of collision results in the colliding bodies moving off together?
Answer: C
In a perfectly inelastic collision, the objects stick together and move with one common velocity afterward.
29.If the mass of an object doubles while its velocity stays the same, its momentum:
Answer: B
Since p = mv, doubling the mass while velocity is unchanged doubles the momentum.
30.On a force–time graph, the area under the graph represents:
Answer: A
Since impulse J = FΔt, the area under a force-time graph gives the total impulse.
31.Momentum is conserved only during elastic collisions.
Answer: False
Momentum is conserved in any isolated collision, whether elastic or inelastic; only kinetic energy conservation is limited to elastic collisions.
32.In a perfectly inelastic collision, the colliding objects move together with a common velocity after impact.
Answer: True
This is the defining feature of a perfectly inelastic collision.
33.Impulse is equal to the rate of change of momentum.
Answer: False
Impulse equals the total change in momentum (J = Δp); it is force, not impulse, that equals the rate of change of momentum.
34.A rocket can accelerate in the vacuum of space because momentum is conserved between the rocket and the expelled exhaust gases.
Answer: True
The rocket does not need air to push against; it moves forward as expelled gases carry momentum backward, conserving total momentum.
35.Kinetic energy is always conserved in every type of collision.
Answer: False
Kinetic energy is conserved only in elastic collisions; in inelastic collisions, some kinetic energy is converted to heat, sound, or deformation.
36.The SI unit of momentum is ______.
Answer: kg·m/s
Momentum is mass (kg) times velocity (m/s), giving units of kg·m/s.
37.The product of force and the time for which it acts is called ______.
Answer: impulse
Impulse (J = FΔt) measures the overall effect of a force acting over a time interval.
38.A collision in which the colliding objects stick together and move as one is called a(n) ______ collision.
Answer: perfectly inelastic
This type of collision conserves momentum but not kinetic energy, as the objects combine and move together.
39.The law of conservation of momentum states that the total momentum of an isolated system remains ______.
Answer: constant
As long as no external force acts on the system, its total momentum does not change over time.
40.The backward movement of a gun when it is fired is called ______.
Answer: recoil
Recoil occurs because momentum is conserved: the gun moves backward with momentum equal and opposite to the bullet's forward momentum.
1.What is meant by an 'energy source'?
Answer: C
An energy source is anything (natural or man-made) that provides energy which can be converted into a useful form, such as electricity or heat.
2.Which of the following is a renewable energy source?
Answer: D
Solar energy is renewable because sunlight is continuously and naturally replenished, unlike fossil fuels.
3.Which of the following is a non-renewable energy source?
Answer: A
Coal is a fossil fuel formed over millions of years and cannot be replenished within a human lifetime, making it non-renewable.
4.Which device converts sunlight directly into electricity?
Answer: A
Solar panels use photovoltaic cells to convert sunlight directly into electrical energy.
5.A wind turbine converts:
Answer: B
Wind turbines use blades turned by moving air to drive a generator, converting kinetic energy into electricity.
6.Hydroelectric power is generated using the energy of:
Answer: D
Hydroelectric plants use the kinetic and potential energy of moving/falling water to turn turbines and generate electricity.
7.Which of these is an example of biomass energy?
Answer: C
Biomass energy comes from organic materials such as wood, crop residues, and animal waste, which can be burned or converted into fuel.
8.Geothermal energy is derived from:
Answer: B
Geothermal energy comes from the natural heat produced within the Earth's crust and interior.
9.Which gas released from burning fossil fuels is the main contributor to global warming?
Answer: D
Carbon dioxide (CO2) is a major greenhouse gas released when fossil fuels are burned, and it traps heat in the atmosphere.
10.Fossil fuels (coal, oil, natural gas) were formed from:
Answer: A
Fossil fuels form from the buried, decomposed remains of ancient organisms subjected to heat and pressure over millions of years.
11.Why are fossil fuels considered non-renewable?
Answer: C
Because fossil fuels form over geological timescales, the supply on Earth is finite and cannot be replenished quickly.
12.Which gases mainly cause acid rain when released from burning fossil fuels?
Answer: C
Sulfur dioxide and nitrogen oxides react with water vapour in the atmosphere to form acidic compounds that fall as acid rain.
13.Rwanda generates a significant part of its electricity from which renewable source?
Answer: D
Rwanda relies heavily on hydropower plants (e.g., on the Rusizi, Nyabarongo, and other rivers) for a large share of its electricity.
14.What valuable energy resource is found dissolved in the deep waters of Lake Kivu?
Answer: C
Lake Kivu contains large amounts of dissolved methane gas that can be extracted and used to generate electricity.
15.Which renewable energy source has strong potential in Rwanda due to its sunny climate?
Answer: C
Rwanda receives abundant sunlight throughout the year, giving it strong potential for solar power generation.
16.'Energy security' in the context of renewable energy transition mainly refers to:
Answer: B
Energy security means ensuring a dependable, adequate, and stable energy supply, which renewables can strengthen by reducing dependence on imported fuels.
17.How can renewable energy support rural development?
Answer: B
Small-scale and off-grid renewable systems, such as solar home systems, can provide electricity to remote communities without extending the national grid.
18.Which of the following is an economic benefit of switching to renewable energy?
Answer: D
Renewable energy projects can create local jobs and reduce a country's need to spend money importing fossil fuels.
19.How does using renewable energy benefit public health?
Answer: A
Renewable sources like solar and wind produce little to no air pollution, reducing respiratory and cardiovascular illnesses linked to burning fossil fuels.
20.Climate change is primarily driven by:
Answer: B
The buildup of greenhouse gases (especially CO2) from burning fossil fuels traps more heat in the atmosphere, driving climate change.
21.Which of the following energy sources is NOT a fossil fuel?
Answer: A
Coal, oil, and natural gas are fossil fuels formed from ancient organic matter, while solar energy comes directly from sunlight and is renewable.
22.Wind is generated mainly due to:
Answer: B
Differences in solar heating across the Earth's surface create pressure differences that cause air to move as wind.
23.The water cycle that powers hydroelectricity is ultimately driven by energy from:
Answer: B
Solar energy evaporates water, which later falls as rain and flows through rivers, making hydropower indirectly solar-driven.
24.Which of the following is a common cause of water pollution linked to non-renewable energy sources?
Answer: D
Oil spills from drilling, transportation, or storage accidents can severely pollute rivers, lakes, and oceans.
25.How is nuclear energy typically classified?
Answer: B
Nuclear power relies on uranium, a finite mineral resource, so it is generally classified as non-renewable, even though it produces low CO2 emissions.
26.What is a major disadvantage of solar energy as a power source?
Answer: A
Solar power generation drops at night and during cloudy weather, making it an intermittent (variable) energy source.
27.What is a key advantage of wind energy over fossil fuels?
Answer: C
Wind energy generates electricity without burning any fuel and without direct greenhouse gas emissions, though it depends on wind availability.
28.Which of the following best explains 'sustainability' in relation to energy sources?
Answer: D
Sustainable energy use meets current needs while preserving resources and the environment for future generations.
29.Deforestation for fuelwood in some parts of Rwanda is linked mainly to reliance on which energy source?
Answer: A
Heavy reliance on wood and charcoal (biomass) for cooking and heating can lead to deforestation if not managed sustainably.
30.Which of the following best describes 'energy transition' as taught in this unit?
Answer: A
Energy transition refers to the gradual move away from fossil fuels toward cleaner, renewable energy sources for sustainability, security, and health reasons.
31.Non-renewable energy sources can be replenished within a human lifetime.
Answer: False
Non-renewable sources such as coal, oil, and natural gas take millions of years to form, so they cannot be replenished quickly.
32.Burning coal releases carbon dioxide, which contributes to global warming.
Answer: True
Coal is a carbon-rich fossil fuel, and burning it releases significant amounts of CO2 into the atmosphere.
33.Geothermal energy comes from heat stored inside the Earth.
Answer: True
Geothermal energy is harnessed from the natural heat found within the Earth's crust and interior.
34.Rwanda has little to no potential for solar power because of insufficient sunlight.
Answer: False
Rwanda actually receives abundant sunlight throughout the year, giving it strong potential for solar energy development.
35.Methane gas extracted from Lake Kivu can be used to generate electricity.
Answer: True
Methane gas dissolved in Lake Kivu is extracted and used as fuel in gas-powered plants to generate electricity for Rwanda.
36.Energy sources that can be naturally replenished within a short period of time are called ______ energy sources.
Answer: renewable
Renewable sources such as solar, wind, hydro, biomass, and geothermal are continuously or quickly replenished by nature.
37.Coal, oil, and natural gas are collectively known as ______.
Answer: fossil fuels
These non-renewable resources formed from the remains of ancient organisms over millions of years.
38.The gradual increase in the Earth's average temperature caused by greenhouse gases is called ______.
Answer: global warming (climate change)
Greenhouse gases such as CO2 trap heat in the atmosphere, leading to a rise in average global temperatures over time.
39.In Rwanda, ______ gas dissolved in Lake Kivu is being extracted and used to generate electricity.
Answer: methane
This resource provides Rwanda with a locally available fuel for electricity generation.
40.The trapping of heat in the Earth's atmosphere by certain gases is known as the ______ effect.
Answer: greenhouse
The greenhouse effect is a natural process that becomes intensified by human emissions of gases like carbon dioxide and methane.
1.What is meant by the 'heat capacity' of an object?
Answer: C
Heat capacity (C) is the quantity of heat required to raise the temperature of a specific object (of given mass) by 1°C, C = Q/ΔT.
2.What is 'specific heat capacity' (c) of a substance?
Answer: B
Specific heat capacity is the amount of heat energy required to raise the temperature of 1 kg of a substance by 1°C (or 1 K).
3.What is the SI unit of specific heat capacity?
Answer: D
Specific heat capacity is expressed in joules per kilogram per degree Celsius, J/(kg·°C), equivalent to J/(kg·K).
4.Calculate the heat required to raise the temperature of 2 kg of water (c = 4200 J/(kg·°C)) by 10°C.
Answer: B
Q = mcΔT = 2 × 4200 × 10 = 84,000 J.
5.A substance of mass 0.5 kg and specific heat capacity 2000 J/(kg·°C) absorbs 5000 J of heat. Find its temperature rise.
Answer: A
ΔT = Q/(mc) = 5000/(0.5 × 2000) = 5000/1000 = 5°C.
6.A 1 kg substance absorbs 8400 J of heat and its temperature rises by 2°C. What is its specific heat capacity?
Answer: D
c = Q/(mΔT) = 8400/(1 × 2) = 4200 J/(kg·°C).
7.Compared to most common metals, water has a specific heat capacity that is:
Answer: A
Water's specific heat capacity (about 4200 J/(kg·°C)) is much higher than that of metals like iron (about 450 J/(kg·°C)), so water heats up and cools down more slowly.
8.What are the three main modes of heat transfer?
Answer: A
Heat can be transferred by conduction, convection, and radiation.
9.Conduction of heat mainly occurs in:
Answer: D
Conduction transfers heat through direct particle-to-particle contact, which is most effective in solids where particles are closely packed.
10.Convection of heat mainly occurs in:
Answer: D
Convection involves the physical movement of heated fluid (liquid or gas), so it occurs in fluids, not solids.
11.Radiation as a mode of heat transfer:
Answer: D
Radiation transfers heat via electromagnetic waves and can travel through empty space (a vacuum), unlike conduction and convection.
12.Which mode of heat transfer does NOT require a medium?
Answer: C
Radiation is unique among the three modes because it can transfer heat energy through a vacuum, such as from the Sun to the Earth.
13.Heat travelling along a metal spoon left in hot soup is an example of:
Answer: B
Heat passes directly through the metal particles of the spoon by conduction.
14.The rising and circulating currents in a pot of boiling water are an example of:
Answer: A
As water is heated, warmer, less dense water rises and cooler water sinks, creating convection currents.
15.Heat reaching the Earth from the Sun travels mainly by:
Answer: B
Since space is a vacuum, the Sun's heat can only reach Earth by radiation (electromagnetic waves).
16.Which of these materials is generally the best conductor of heat?
Answer: A
Metals such as copper have free electrons that allow heat to be conducted very efficiently.
17.Materials that conduct heat poorly, such as wood, plastic, and air, are called:
Answer: D
Poor conductors of heat are known as insulators, since they slow down or resist the flow of heat.
18.What is 'latent heat'?
Answer: B
Latent heat is the energy absorbed or released when a substance changes state (e.g., melting, boiling) while its temperature stays constant.
19.Which formula is used to calculate the quantity of heat involved in a change of state?
Answer: A
The heat needed for a phase change is Q = mL, where L is the specific latent heat of fusion or vaporisation.
20.Calculate the heat required to melt 2 kg of ice completely, given the specific latent heat of fusion of ice is 334,000 J/kg.
Answer: D
Q = mL = 2 × 334,000 = 668,000 J.
21.Calculate the heat needed to vaporise 0.5 kg of water at its boiling point, given the specific latent heat of vaporisation is 2,260,000 J/kg.
Answer: A
Q = mL = 0.5 × 2,260,000 = 1,130,000 J.
22.During a change of state (e.g., ice melting to water), what happens to the temperature of the substance?
Answer: B
While a substance is changing state, all the heat energy goes into breaking or forming bonds between particles, so the temperature stays constant.
23.The change of state from solid to liquid is called:
Answer: C
Melting (also called fusion) is the process by which a solid changes into a liquid when heated.
24.The change of state from liquid to gas is called:
Answer: C
Vaporisation is the process by which a liquid changes into a gas, occurring through boiling or evaporation.
25.The change of state from gas to liquid is called:
Answer: B
Condensation is the process by which a gas loses energy and turns back into a liquid.
26.The change of state from liquid to solid is called:
Answer: C
Freezing (solidification) occurs when a liquid loses heat and turns into a solid.
27.Thermal expansion refers to:
Answer: B
When most substances are heated, their particles vibrate more and move slightly farther apart, causing the material to expand.
28.Which formula describes the linear expansion of a solid?
Answer: C
Linear expansion is given by ΔL = αL₀ΔT, where α is the coefficient of linear expansion, L₀ the original length, and ΔT the temperature change.
29.A metal rod of length 2 m has a coefficient of linear expansion of 12 × 10⁻⁶ /°C. Find its increase in length when heated through 50°C.
Answer: A
ΔL = αL₀ΔT = (12×10⁻⁶) × 2 × 50 = 0.0012 m (1.2 mm).
30.Why are small gaps left between sections of railway tracks?
Answer: C
Gaps allow the metal rails to expand safely when heated, preventing the track from buckling or bending in hot weather.
31.The specific heat capacity of water is higher than that of iron.
Answer: True
Water has a specific heat capacity of about 4200 J/(kg·°C), much higher than iron's approximately 450 J/(kg·°C).
32.During a change of state, the temperature of a substance keeps rising as more heat is added.
Answer: False
During a change of state, temperature remains constant; the added heat (latent heat) is used to change the state, not to raise temperature.
33.Conduction is the main mode of heat transfer in gases.
Answer: False
Convection is the main mode of heat transfer in gases and liquids, since their particles can move freely; conduction dominates in solids.
34.A bimetallic strip bends when heated because the two metals it is made of expand at different rates.
Answer: True
Because the two metals have different coefficients of expansion, uneven expansion causes the strip to bend when heated.
35.Radiation requires a medium, such as air or metal, to transfer heat.
Answer: False
Radiation is the only mode of heat transfer that does not need a medium; it can pass through a vacuum, as heat from the Sun does.
36.The quantity of heat required to change the temperature of a substance without changing its state is calculated using Q = ______.
Answer: mcΔT
This formula uses the mass (m), specific heat capacity (c), and temperature change (ΔT) of the substance.
37.The heat absorbed or released during a change of state at constant temperature is called ______ heat.
Answer: latent
Latent heat is 'hidden' heat that changes a substance's state (solid, liquid, gas) without changing its temperature.
38.Metals allow heat to pass through them easily because they are good ______ of heat.
Answer: conductors
Metals have free electrons that transfer thermal energy quickly, making them good conductors.
39.The transfer of heat through a fluid by the movement of the heated fluid itself is called ______.
Answer: convection
Convection occurs when warmer, less dense fluid rises and cooler, denser fluid sinks, creating a circulating current.
40.Small gaps are left between sections of railway tracks to allow for the ______ of the metal in hot weather.
Answer: (thermal) expansion
Without these gaps, the rails would be unable to expand safely and could buckle when heated.
1.What is atmospheric pressure?
Answer: B
Atmospheric pressure is the pressure exerted on a surface by the weight of the column of air above it.
2.The average atmospheric pressure at sea level is approximately:
Answer: B
Standard atmospheric pressure at sea level is about 101,325 Pa, often rounded to 1.013 × 10^5 Pa (76 cmHg).
3.Which instrument is used to measure atmospheric pressure?
Answer: C
A barometer (mercury or aneroid) is the instrument used to measure atmospheric pressure.
4.In a simple mercury barometer, atmospheric pressure is measured by:
Answer: C
Atmospheric pressure pushes mercury up an evacuated tube; the height of the supported column indicates the pressure (about 76 cm at sea level).
5.As altitude increases, atmospheric pressure:
Answer: C
At higher altitude there is less air above a point, so the weight of the overlying air column, and hence pressure, decreases.
6.Why is it harder to breathe at the top of a very high mountain?
Answer: B
Lower atmospheric pressure at high altitude means air (and oxygen) is less dense, making breathing more difficult.
7.How does an increase in air temperature generally affect atmospheric pressure in a region?
Answer: B
When air is heated it expands and its density falls, which is associated with a drop in local atmospheric pressure (rising warm air creates low-pressure zones).
8.A region of low atmospheric pressure is often associated with unsettled, stormy weather.
Answer: True
Low-pressure systems are linked to rising air, cloud formation and unstable, often stormy weather, while high pressure is linked to fine, settled weather.
9.An aneroid barometer measures atmospheric pressure using:
Answer: B
An aneroid barometer contains a flexible sealed metal capsule that expands or contracts with changing atmospheric pressure, moving a needle on a scale.
10.The scientist who first demonstrated that atmospheric pressure could support a column of mercury, giving his name to the unit torr, was ______.
Answer: Torricelli
Evangelista Torricelli performed the classic mercury barometer experiment in 1643.
11.When you suck on a drinking straw placed in a drink, the liquid rises because:
Answer: A
Sucking reduces the air pressure inside the straw; the higher atmospheric pressure acting on the drink's surface then pushes the liquid up into the straw.
12.A simple hand (lift) pump raises water from a well mainly because of:
Answer: A
As the piston rises, it lowers the pressure above the water; atmospheric pressure acting on the water in the well pushes it up into the pump.
13.A siphon can be used to transfer liquid from a higher container to a lower one over an intervening rise mainly because of:
Answer: A
Once the tube is filled with liquid, atmospheric pressure and the weight of the falling liquid column maintain continuous flow from the higher to the lower level.
14.A siphon tube must be completely filled with liquid (primed) before it will work continuously.
Answer: True
Air pockets break the continuous liquid column needed for atmospheric pressure and gravity to drive the flow, so the tube must first be filled with liquid.
15.A vacuum cleaner picks up dust because:
Answer: D
The internal fan lowers the air pressure inside the cleaner; higher atmospheric pressure outside forces air and dust in through the nozzle to equalize pressure.
16.A rubber sucker sticks to a smooth wall because:
Answer: C
Squeezing out the air lowers pressure under the sucker; atmospheric pressure pushing on the outer surface then holds the sucker firmly against the wall.
17.A rubber pipette works by squeezing the bulb to expel air, then releasing it so that ______ pressure pushes liquid up into the tube.
Answer: atmospheric
Releasing the squeezed bulb lowers internal pressure, and atmospheric pressure outside pushes liquid up into the pipette.
18.During inhalation (breathing in), what happens inside the chest cavity?
Answer: D
Diaphragm contraction increases chest volume, lowering internal pressure below atmospheric pressure, so air flows into the lungs to equalize pressure.
19.During exhalation (breathing out), the pressure inside the lungs becomes:
Answer: D
The diaphragm relaxes, chest volume decreases, and lung pressure rises above atmospheric pressure, forcing air out.
20.Which of these is NOT a common application of atmospheric pressure?
Answer: C
A transformer works on electromagnetic induction, not atmospheric pressure; the other three all rely on atmospheric pressure differences.
21.State Archimedes' principle.
Answer: A
Archimedes' principle: the upthrust on a body immersed in a fluid equals the weight of the fluid displaced by the body.
22.The upward force exerted by a fluid on a body immersed in it is called:
Answer: D
This upward force is called upthrust or buoyant force, and results from the pressure difference between the top and bottom of the submerged body.
23.The formula for upthrust on a fully submerged object is:
Answer: A
Upthrust equals the weight of fluid displaced: U = ρ_fluid × V_displaced × g, where V_displaced is the volume of fluid pushed aside.
24.A block of volume 0.002 m³ is fully submerged in water (density 1000 kg/m³). Taking g = 10 N/kg, the upthrust on it is:
Answer: B
U = ρVg = 1000 × 0.002 × 10 = 20 N.
25.An object weighs 50 N in air and 30 N when fully submerged in water. The upthrust on the object is:
Answer: A
Upthrust = apparent weight loss = weight in air − weight in water = 50 N − 30 N = 20 N.
26.A body floats in a fluid when:
Answer: A
A floating object displaces just enough fluid so that the upthrust equals its weight, which happens when its average density is less than or equal to that of the fluid.
27.A body sinks in a fluid when:
Answer: D
If the object's density is greater than the fluid's density, even full displacement cannot produce enough upthrust to balance its weight, so it sinks.
28.The apparent loss of weight of an object when immersed in a liquid is equal to the upthrust acting on it.
Answer: True
By Archimedes' principle, the difference between the weight in air and the weight in the liquid equals the upthrust from the displaced liquid.
29.The upward force experienced by an object immersed in a fluid is also known as the ______ force.
Answer: buoyant
Upthrust is commonly called the buoyant force.
30.The SI unit of upthrust is the:
Answer: B
Upthrust is a force, so it is measured in newtons (N), like weight.
31.A stone of volume 500 cm³ (5 × 10^-4 m³) is fully submerged in water (density 1000 kg/m³, g = 10 N/kg). The upthrust on the stone is:
Answer: C
U = ρVg = 1000 × 5×10^-4 × 10 = 5 N.
32.Upthrust on a submerged object always acts:
Answer: D
Upthrust arises because fluid pressure increases with depth, so pressure on the bottom of the object exceeds that on top, giving a net upward force.
33.Ships made of steel, which is denser than water, are able to float mainly because:
Answer: C
The hollow hull encloses a large volume of air, so the ship's overall average density is lower than water, allowing the upthrust to balance its weight.
34.A hydrometer is used to:
Answer: C
A hydrometer floats in a liquid; the depth to which it sinks depends on the liquid's density, and its calibrated stem reads the density directly.
35.A hydrometer floats lower (sinks deeper) in a liquid of lower density than in a liquid of higher density.
Answer: True
In a less dense liquid, more volume must be displaced to generate enough upthrust to balance the hydrometer's weight, so it sinks deeper.
36.A hot air balloon rises because:
Answer: A
Heated air inside the envelope is less dense than the surrounding cooler air; the resulting upthrust exceeds the total weight, so the balloon rises.
37.A life jacket helps a person float in water mainly by:
Answer: B
The low-density buoyant material increases volume without adding much weight, lowering the average density of the wearer so that upthrust can support their weight.
38.A solid iron nail sinks in water, but a hollow iron ship floats, because the ship's overall average ______ is lower than that of water.
Answer: density
Spreading the same mass of iron over a much larger hollow volume lowers the ship's average density below that of water, unlike a solid nail.
39.When a ship is loaded beyond its safe limit, it:
Answer: D
Extra weight requires displacing more water to generate enough upthrust, so the ship sits lower; beyond the safe load line it risks taking on water and sinking.
40.Life jackets are typically made from ______-density buoyant material such as foam so that they increase volume without adding much weight.
Answer: low
Low-density foam materials give a large volume for little added mass, increasing buoyancy.
1.When resistors are connected in series in a circuit, the total resistance is:
Answer: A
For resistors in series: R_total = R1 + R2 + R3 + ... , since the same current flows through each in turn.
2.Three resistors of 2 Ω, 3 Ω and 5 Ω are connected in series. The total resistance is:
Answer: B
In series, resistances add: 2 + 3 + 5 = 10 Ω.
3.In a series circuit, the current flowing through each resistor is:
Answer: D
There is only one path for current in a series circuit, so the same current flows through every component.
4.For resistors connected in parallel, the formula for total resistance is:
Answer: D
For resistors in parallel, the reciprocals of resistance add: 1/R_total = 1/R1 + 1/R2 + ...
5.Two resistors of 4 Ω and 6 Ω are connected in parallel. The total resistance is:
Answer: D
1/R = 1/4 + 1/6 = 3/12 + 2/12 = 5/12, so R = 12/5 = 2.4 Ω.
6.In a parallel circuit, the voltage across each branch is:
Answer: D
All branches in parallel are connected between the same two points, so each branch has the same voltage as the supply.
7.Adding more resistors in parallel always decreases the total (equivalent) resistance of the combination.
Answer: True
Each extra parallel path provides an additional route for current, so the total resistance of a parallel combination is always less than the smallest individual resistor.
8.The electromotive force (e.m.f.) of a cell or battery is best described as:
Answer: A
E.m.f. is the total energy per unit charge supplied by the source, measured in volts, before any internal voltage drop is subtracted.
9.Internal resistance of a battery causes:
Answer: A
As current flows through the battery's internal resistance, some energy is lost inside the cell, so terminal voltage V = E.m.f. − I×r, which is less than the e.m.f.
10.A battery has an e.m.f. of 12 V and internal resistance of 0.5 Ω. When it delivers a current of 2 A, its terminal voltage is:
Answer: D
Terminal voltage V = E − I×r = 12 − (2 × 0.5) = 12 − 1 = 11 V.
11.The equation relating terminal voltage V, e.m.f. E, current I and internal resistance r is V = E − I × ______.
Answer: r
Terminal voltage equals e.m.f. minus the voltage drop across the internal resistance (I×r).
12.Why does a battery's terminal voltage drop when it supplies a larger current?
Answer: A
A larger current causes a larger voltage drop (I×r) across the internal resistance, reducing the voltage available at the terminals.
13.In household electrical installation, the point where electricity from the supply company first enters the building is called the:
Answer: C
The service entrance, or main supply point, is where the utility's cables connect to the building's own wiring system.
14.The device that records the amount of electrical energy (in kWh) consumed in a house is the:
Answer: A
The energy meter measures and records electrical energy used, in kilowatt-hours, for billing purposes.
15.The distribution board (consumer unit) in a house mainly functions to:
Answer: C
The distribution board splits the incoming supply into separate circuits (lighting, sockets, etc.), each protected by its own breaker or fuse.
16.Circuit breakers and fuses in a house wiring system are mainly used to:
Answer: C
They protect the circuit and wiring by breaking the circuit if the current becomes dangerously high, for example due to a short circuit or overload.
17.The earthing (grounding) system in a house installation is designed to:
Answer: B
Earthing connects exposed metal parts of appliances to the ground, so a fault current flows safely to earth instead of through a person, and can trip protection devices.
18.Conduits used in electrical installation are mainly meant to:
Answer: D
Conduits are tubes (metal or plastic) that house and protect cables from mechanical damage, moisture and fire hazards.
19.In a house circuit, a switch is used to:
Answer: B
A switch is a control device that makes or breaks the circuit, turning the connected load on or off.
20.Sockets (outlets) in a house wiring system serve to:
Answer: C
Sockets allow appliances to be safely connected to the household electrical supply via plugs.
21.Lighting points and socket outlets in a house are typically wired as completely separate circuits from the main distribution board.
Answer: True
Lighting circuits and socket (power) circuits are usually wired separately, each with its own protective device, so a fault in one does not affect the other.
22.A protective device that automatically opens the circuit when current exceeds a set value, and can be manually reset afterward, is called a circuit ______.
Answer: breaker
Unlike a fuse (which must be replaced), a circuit breaker can be reset and reused after tripping.
23.During house wiring installation, 'termination and connection of cables' refers to:
Answer: A
Termination involves preparing cable ends and firmly and safely connecting them to terminals, ensuring good electrical contact and mechanical security.
24.'Mounting fixtures and accessories' in the installation process includes:
Answer: C
This stage involves physically fitting and securing switches, sockets, lamp holders and other accessories in place.
25.'Earthing and bonding' during installation mainly involves:
Answer: C
Bonding connects metal parts (pipes, enclosures, casings) to earth so they cannot become dangerously live during a fault.
26.Before energizing a newly installed house wiring system, electricians should first carry out:
Answer: B
Testing (continuity, insulation resistance, polarity, earth continuity) confirms the installation is safe and correctly wired before it is switched on.
27.'Energizing the system' in the installation process means:
Answer: B
Energizing is turning on the electrical supply to the installation only after it has passed all required safety tests and inspections.
28.'Documentation and handover' at the end of an installation project typically includes:
Answer: D
Proper documentation (circuit diagrams, test results, certificates) is handed to the client so the installation can be maintained and understood in future.
29.Testing and inspection of a house wiring installation should be done only after the system has already been energized and used for several months.
Answer: False
Testing and inspection must be carried out before energizing the system, to ensure the installation is safe prior to first use.
30.The stage of house wiring in which metal parts are connected together and to earth to prevent dangerous voltages on exposed metal is called earthing and ______.
Answer: bonding
Bonding links metal parts electrically to the earthing system so they remain at the same (safe) potential.
31.Why is earthing important for electrical safety in a house?
Answer: A
If a live wire touches an earthed metal casing, most fault current flows safely to earth rather than through a person, and the resulting large current trips the fuse or breaker.
32.A fuse protects a circuit by:
Answer: C
A fuse contains a thin wire that melts (and breaks the circuit) when current exceeds a safe rated value, preventing overheating and fire.
33.Compared with a fuse, a circuit breaker's main advantage is that it:
Answer: B
Unlike a fuse, which must be replaced after melting, a circuit breaker is a mechanical/electromagnetic switch that can simply be reset after a fault is cleared.
34.An electric appliance without a properly earthed metal casing poses a danger because:
Answer: B
Without earthing, a fault connecting a live wire to the casing has no safe path to ground, so the casing stays dangerously live until someone touches it, completing the shock circuit.
35.Why should fuse ratings match the appliance or circuit they protect, rather than always using the highest available rating?
Answer: B
If the fuse rating is too high for the wiring or appliance, it may allow a dangerous overcurrent to continue flowing without blowing, risking overheating or fire.
36.Circuit breakers and fuses serve the same basic safety purpose: disconnecting a circuit when current becomes dangerously high.
Answer: True
Both devices are protection devices designed to interrupt current when it exceeds a safe level, though they differ in mechanism and reusability.
37.A cell's internal ______ causes the terminal voltage to be lower than the e.m.f. whenever current flows through the cell.
Answer: resistance
Internal resistance produces a voltage drop (I×r) inside the cell itself, reducing the voltage available at its terminals.
38.A protection device that quickly disconnects a circuit if it detects a small leakage (earth fault) current, offering extra shock protection, is called a(n):
Answer: C
An RCD (or ELCB) monitors for small imbalances in current that indicate leakage to earth and disconnects the circuit rapidly to protect against electric shock.
39.Which combination correctly matches series and parallel circuit properties?
Answer: A
In series circuits current is the same throughout while voltage splits across components; in parallel circuits voltage is the same across each branch while current splits between them.
40.A wiring/cable used in house installation must be correctly sized (cross-sectional area) mainly because:
Answer: D
A cable that is too thin for the current it must carry has higher resistance and heats up excessively, which can damage insulation and cause a fire; correct sizing keeps the cable within a safe current-carrying capacity.
1.A transformer is a device that mainly works on the principle of:
Answer: D
A transformer transfers electrical energy between coils through a changing magnetic field, based on electromagnetic induction (Faraday's law).
2.The three main components of a simple transformer are:
Answer: C
A transformer consists of a primary winding, a secondary winding, and a laminated soft iron core that links them magnetically.
3.A step-up transformer is one that:
Answer: D
A step-up transformer has more turns on the secondary than the primary (Ns > Np), producing a higher output voltage than the input voltage.
4.A step-down transformer is one that:
Answer: A
A step-down transformer has fewer turns on the secondary than the primary (Ns < Np), so it lowers the voltage from input to output.
5.The turns-ratio equation for an ideal transformer is:
Answer: A
For an ideal transformer, the ratio of primary to secondary voltage equals the ratio of primary to secondary number of turns: Vp/Vs = Np/Ns.
6.A transformer has 1000 turns on the primary and 100 turns on the secondary. If the primary voltage is 240 V, the secondary voltage is:
Answer: C
Vs = Vp × (Ns/Np) = 240 × (100/1000) = 24 V, so this is a step-down transformer.
7.A step-up transformer has a primary voltage of 240 V and primary current of 2 A. If it is ideal (100% efficient) and steps the voltage up to 480 V, the secondary current is:
Answer: D
For an ideal transformer, input power = output power: Vp×Ip = Vs×Is, so Is = (240×2)/480 = 480/480 = 1 A.
8.In an ideal transformer, increasing the output voltage (stepping up) also increases the output current proportionally.
Answer: False
In an ideal transformer power is conserved (Vp Ip = Vs Is), so stepping up voltage causes current to decrease proportionally, not increase.
9.The efficiency of a transformer is defined as:
Answer: B
Efficiency compares useful output power to the power supplied: Efficiency = (Output power / Input power) × 100%.
10.A transformer receives 1000 W of input power and delivers 900 W of useful output power. Its efficiency is:
Answer: D
Efficiency = (900/1000) × 100% = 90%.
11.Real transformers are less than 100% efficient mainly because of:
Answer: D
Some electrical energy is converted to heat due to winding resistance (copper loss) and losses in the iron core (hysteresis and eddy current losses), reducing overall efficiency.
12.In a transformer, the core is made of laminated (thin, insulated) sheets of soft iron mainly to reduce ______ current losses.
Answer: eddy
Laminating the core into thin insulated sheets reduces the paths for eddy currents to flow, cutting energy losses as heat.
13.A transformer cannot be used to step up or step down a steady direct current (DC) voltage because:
Answer: A
Transformers rely on a continuously changing magnetic flux to induce voltage in the secondary coil; steady DC produces a constant flux, so no induction (and hence no transformer action) occurs.
14.Which quantity remains theoretically the same between the primary and secondary sides of an ideal transformer?
Answer: A
An ideal transformer has no energy losses, so input electrical power equals output electrical power (Vp Ip = Vs Is), even though voltage and current individually change.
15.Electric power is transmitted over long distances at very high voltage mainly to:
Answer: B
Since power P = VI, transmitting at high voltage allows the same power to be carried with a much smaller current, greatly reducing resistive (I²R) losses in the lines.
16.The typical order of components in an electric power transmission system, from generation to the consumer, is:
Answer: B
Power is generated at the power station, stepped up for efficient long-distance transmission, then stepped down at substations before being distributed to consumers.
17.Step-up transformers are typically located:
Answer: B
Step-up transformers at the generating station raise the voltage produced by generators to a high level suitable for efficient long-distance transmission.
18.Step-down transformers are mainly found at:
Answer: C
Substations use step-down transformers to reduce the high transmission voltage to lower voltages suitable and safe for industrial, commercial and household use.
19.Transformers are used in a national electricity grid both to step voltage up for transmission and to step it down for safe use by consumers.
Answer: True
Step-up transformers raise voltage for efficient transmission, while step-down transformers at substations lower it again to usable, safer levels for consumers.
20.The overall system that carries electrical power from the generating station to consumers, including transformers and cables, is called the electric power ______ system.
Answer: transmission
This describes the electric power transmission (and distribution) system linking generation to end users.
21.Which of the following is an advantage of overhead power transmission lines compared with underground cables?
Answer: A
Overhead lines cost less to install and it is generally easier to spot and fix faults compared with buried underground cables.
22.Which of the following is a disadvantage of overhead transmission lines?
Answer: D
Overhead lines are exposed to the elements, which can cause faults during storms, and their accessibility increases the risk of accidental contact or damage.
23.An advantage of underground power cables over overhead lines is that they:
Answer: B
Buried cables are shielded from wind, storms and lightning, and they avoid the unsightly pylons and wires of overhead lines.
24.A major disadvantage of underground power cables compared with overhead lines is that they:
Answer: C
Underground cables require more expensive insulation, trenching and specialised techniques, making installation and fault repair more costly and time-consuming than overhead lines.
25.Underground cables are generally preferred over overhead lines in busy urban areas partly because they reduce visual impact and risk of accidental contact.
Answer: True
Although more costly, underground cables are often used in cities to avoid unsightly overhead wiring and reduce the danger of people or vehicles contacting live lines.
26.One major cause of power loss in transmission lines is:
Answer: B
As current flows through the resistance of transmission line conductors, electrical energy is converted to heat, described by the formula P = I²R.
27.A transmission line has a total resistance of 5 Ω and carries a current of 10 A. The power lost as heat in the line is:
Answer: C
Power loss P = I²R = 10² × 5 = 100 × 5 = 500 W.
28.If the current in a transmission line is doubled while its resistance stays the same, the I²R power loss becomes:
Answer: D
Since power loss is proportional to the square of current (P = I²R), doubling the current increases the loss by a factor of 2² = 4.
29.Corona discharge, a source of power loss in high-voltage transmission lines, is best described as:
Answer: C
At very high voltages, the electric field around the conductor can ionize the surrounding air, causing a faint glow and energy loss called corona discharge, worsened by humidity.
30.Leakage current as a cause of transmission line power loss refers to:
Answer: A
Leakage currents pass through imperfect insulation (e.g., insulators on pylons) to earth, wasting some of the transmitted electrical energy.
31.The formula used to calculate resistive power loss in a transmission line, where I is the current and R is the line's resistance, is P = I² × ______.
Answer: R
Resistive power loss is given by P = I²R, showing that loss depends on the square of the current and the line's resistance.
32.Which of the following is an effective way to minimize power losses in electrical transmission lines?
Answer: D
Since P = I²R, transmitting at high voltage reduces the current needed for a given power, which greatly reduces resistive losses.
33.Using conductors made of good conducting materials with low resistivity, such as copper or aluminium, helps to minimize transmission losses because:
Answer: B
Lower resistivity conductors have lower resistance for the same dimensions, which directly reduces the I²R power lost as heat.
34.Increasing the cross-sectional area of a transmission line conductor (using a thicker cable) helps reduce power loss because it:
Answer: B
Resistance is inversely proportional to cross-sectional area (R = ρL/A), so a thicker conductor has lower resistance and therefore lower I²R power loss.
35.Transmitting electrical power at a higher voltage for the same delivered power always reduces the current needed, which in turn reduces I²R power losses.
Answer: True
Since power P = VI, a higher transmission voltage means a lower current is needed to deliver the same power, and since losses depend on I², this significantly cuts resistive losses.
36.Good line design to reduce transmission losses can include:
Answer: C
Proper spacing, good insulation and well-sized, well-maintained conductors reduce leakage, corona discharge and resistive losses.
37.A key reason high-voltage transmission is safer for reducing losses but requires strict safety measures near the lines is that:
Answer: C
Although high voltage reduces I²R losses by lowering current, it also increases the risk of electric arcing and shock, so transmission lines need proper clearance, insulation and warning measures.
38.An everyday application of transformers, besides the national grid, is:
Answer: A
Small step-down transformers (or transformer-based adapters) are used in chargers and adapters to convert mains voltage to the low voltages needed by electronic devices.
39.A transformer whose secondary coil has fewer turns than its primary coil is called a step-______ transformer.
Answer: down
Fewer turns on the secondary than the primary means the output voltage is lower than the input, characteristic of a step-down transformer.
40.In Rwanda's national grid, electricity generated at power plants is stepped up to high voltage before transmission mainly to:
Answer: A
As in any national grid, Rwanda steps up voltage for transmission across the country so that lower current is needed to deliver the same power, reducing resistive losses along the lines before substations step the voltage back down for consumers.
1.What is refraction of light?
Answer: A
Refraction is the change in direction of a light ray as it crosses a boundary between two media of different optical densities, caused by a change in speed.
2.Which of the following is a necessary condition for refraction to occur at a boundary?
Answer: D
Refraction requires a change in optical density between the two media; a ray along the normal changes speed but does not bend.
3.The refractive index of a medium is defined as:
Answer: B
Refractive index n equals the ratio of sine of angle of incidence to sine of angle of refraction, and also equals the ratio of speed of light in vacuum to speed in the medium (n = c/v).
4.Light travels from air into a glass block of refractive index 1.5. If the angle of incidence is 30°, what is the angle of refraction?
Answer: C
sin r = sin i / n = sin30°/1.5 = 0.5/1.5 = 0.333, so r = sin⁻¹(0.333) ≈ 19.5°.
5.The speed of light in vacuum is c and in a medium is v. The refractive index n of the medium is given by:
Answer: A
By definition, the absolute refractive index n = c/v, where c is the speed of light in vacuum and v its speed in the medium.
6.A medium has a refractive index of 1.5. If the speed of light in vacuum is 3 × 10⁸ m/s, what is the speed of light in the medium?
Answer: B
v = c/n = (3 × 10⁸)/1.5 = 2.0 × 10⁸ m/s.
7.A ray of light striking a boundary exactly along the normal changes speed on entering the new medium but does not change direction.
Answer: True
At 0° incidence there is no bending because sin i = sin r = 0, but the speed still changes according to the refractive index of the new medium.
8.Refraction can occur even when the two media have exactly the same optical density.
Answer: False
If the two media have the same optical density (same refractive index), the speed of light does not change, so there is no refraction/bending, even if some transmission occurs.
9.The bending of light as it passes obliquely from one transparent medium into another of different optical density is called ______.
Answer: refraction
This change of direction happens because the speed of light changes when it crosses into a medium of different optical density.
10.When light travels from air (less dense) into glass (denser medium) at an angle, it bends:
Answer: C
Light slows down when entering a denser medium, causing it to bend towards the normal.
11.When light travels from glass (denser) into air (less dense) at an angle, it bends:
Answer: A
Light speeds up when leaving a denser medium for a less dense one, so it bends away from the normal.
12.Snell's law of refraction relating two media of refractive indices n1 and n2 is written as:
Answer: A
Snell's law states that n1 sin i = n2 sin r, where i is the angle of incidence in medium 1 and r is the angle of refraction in medium 2.
13.Light travels from water (n = 1.33) into glass (n = 1.5) with an angle of incidence of 40°. What is the angle of refraction (to 1 d.p.)?
Answer: C
Using n1 sin i = n2 sin r: sin r = (1.33 × sin40°)/1.5 = (1.33 × 0.643)/1.5 ≈ 0.570, so r ≈ 34.8°.
14.According to the first law of refraction, the incident ray, the refracted ray and the normal at the point of incidence:
Answer: C
The first law of refraction states that the incident ray, refracted ray and the normal at the point of incidence all lie in the same plane.
15.The second law of refraction (Snell's law) states that for a given pair of media, the ratio sin i / sin r is a ______ called the refractive index.
Answer: constant
For any two given media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is always the same value, the refractive index.
16.The critical angle for a pair of media is defined as the angle of incidence in the denser medium for which:
Answer: B
The critical angle C is the angle of incidence in the denser medium at which the refracted ray grazes along the boundary, making the angle of refraction exactly 90°.
17.At the critical angle, the angle of refraction in the less dense medium is exactly ______ degrees.
Answer: 90
By definition, the critical angle produces a refracted ray that travels along the boundary between the two media, at 90° to the normal.
18.Total internal reflection occurs only when:
Answer: C
Total internal reflection requires light travelling from a denser medium towards a less dense one, with an angle of incidence greater than the critical angle.
19.A glass has a refractive index of 1.5. What is its critical angle for the glass-air boundary (to 1 d.p.)?
Answer: A
sin C = 1/n = 1/1.5 = 0.667, so C = sin⁻¹(0.667) ≈ 41.8°.
20.Water has a refractive index of 1.33. What is the critical angle for the water-air boundary (to 1 d.p.)?
Answer: C
sin C = 1/n = 1/1.33 = 0.752, so C = sin⁻¹(0.752) ≈ 48.8°.
21.Total internal reflection can occur when light travels from air into glass, provided the angle of incidence is large enough.
Answer: False
Total internal reflection can only occur when light travels from a denser medium into a less dense one (e.g. glass to air), not the reverse.
22.Optical fibres transmit light over long distances mainly by relying on which phenomenon?
Answer: D
Light entering an optical fibre repeatedly strikes the core-cladding boundary at an angle greater than the critical angle, undergoing total internal reflection and travelling along the fibre with little loss.
23.In a simple periscope built with two right-angled prisms instead of mirrors, light is redirected by:
Answer: A
Each prism is arranged so that light strikes its 45° face at an angle greater than the critical angle of glass, undergoing total internal reflection to turn the light through 90°.
24.When a ray of light passes through a glass block with parallel sides (parallel-sided medium), the emergent ray compared with the original incident ray is:
Answer: D
Refraction at the first surface bends the ray towards the normal, and refraction at the second (parallel) surface bends it back by an equal amount, so the emergent ray is parallel to the incident ray but shifted sideways (laterally displaced).
25.When light passes through a glass block with parallel surfaces, the emergent ray is parallel to the incident ray but is shifted sideways; this shift is called the lateral ______.
Answer: displacement
The sideways shift between the incident ray's original path and the emergent ray's path is called the lateral displacement.
26.A converging (convex) lens is:
Answer: D
A converging lens bulges outward and is thicker in the middle than at its edges, which causes parallel rays to bend towards a focal point.
27.A diverging (concave) lens is:
Answer: B
A diverging lens curves inward and is thinner at the centre than at the edges, causing parallel rays to spread out (diverge) as if from a virtual focal point.
28.A diverging lens always produces a virtual, upright and diminished image, regardless of the object's position.
Answer: True
For any real object placed in front of a diverging lens, ray diagrams always show a virtual, upright, diminished image on the same side as the object.
29.The lens equation relating object distance u, image distance v and focal length f is:
Answer: C
The thin lens equation is 1/f = 1/u + 1/v, using the real-is-positive sign convention for a real object and real image.
30.An object is placed 30 cm from a converging lens of focal length 10 cm. Where is the image formed?
Answer: B
1/v = 1/f − 1/u = 1/10 − 1/30 = 3/30 − 1/30 = 2/30, so v = 15 cm.
31.An object is placed 20 cm from a lens, and a real image forms 60 cm from the lens. What is the focal length of the lens?
Answer: D
1/f = 1/u + 1/v = 1/20 + 1/60 = 3/60 + 1/60 = 4/60, so f = 15 cm.
32.A converging lens has a focal length of 25 cm (0.25 m). What is its power?
Answer: C
Power P = 1/f (f in metres) = 1/0.25 = 4 dioptres (D).
33.A diverging lens has a focal length of 50 cm. What is its power?
Answer: B
For a diverging lens, f is negative, so f = −0.5 m and P = 1/f = 1/(−0.5) = −2 D.
34.The power of a lens is measured in units called the ______.
Answer: dioptre
Power P = 1/f, where f is the focal length in metres, and the resulting unit is the dioptre (D).
35.The linear magnification produced by a lens is given by:
Answer: B
Magnification m equals the ratio of image distance to object distance, which is also equal to the ratio of image height to object height (hi/ho).
36.An object 15 cm from a lens produces an image 45 cm from the lens. What is the magnification?
Answer: D
m = v/u = 45/15 = 3, so the image is 3 times the height of the object.
37.When white light passes through a glass prism, it splits into a band of colours. This splitting is called:
Answer: A
Dispersion is the separation of white light into its component colours (a spectrum) because each colour (wavelength) is refracted by a slightly different amount in the prism.
38.In the spectrum produced by a prism, which colour of light is deviated (bent) the most?
Answer: B
Violet light has the shortest wavelength and is refracted by the glass more strongly (highest refractive index for that colour), so it is deviated the most; red is deviated the least.
39.Rainbows are formed in the sky mainly due to which combination of processes acting on sunlight inside water droplets?
Answer: D
Sunlight entering a water droplet is refracted (dispersed into colours), undergoes internal reflection at the back of the droplet, and is refracted again on leaving, spreading the colours out to form a rainbow.
40.A coin lies at the bottom of a pool of water. To an observer looking down from directly above, the coin appears:
Answer: A
Light rays from the coin bend away from the normal as they leave the water and enter air, making the coin appear closer to the surface (shallower) than its real depth; n = real depth/apparent depth.
1.What is communication?
Answer: C
Communication is the process by which information (a message) is transferred from a sender (source) to a receiver through some channel.
2.Digital communication refers to the transfer of information using:
Answer: B
In digital communication, information is converted into discrete binary values (0s and 1s) before being transmitted, rather than being sent as a continuously varying signal.
3.In the basic block diagram of a communication system, the device that converts a message into a signal suitable for transmission is the:
Answer: C
The transmitter takes the original message (e.g. sound or data), processes it and converts it into a signal that can travel through the transmission channel.
4.In a communication system, the medium through which the signal travels from the sender to the receiver is called the:
Answer: A
The channel is the physical or wireless path (such as a cable, optical fibre, or the atmosphere) through which the signal travels from transmitter to receiver.
5.In a communication system, the device that accepts the transmitted signal and converts it back into a usable form of the original message is the:
Answer: C
The receiver picks up the transmitted signal from the channel and converts it back into a form the destination can understand, such as sound or text.
6.The three basic parts of any communication system, in order, are the transmitter, the ______, and the receiver.
Answer: channel
The channel is the transmission path linking the transmitter that sends the signal to the receiver that picks it up.
7.Which of the following is an example of a wired (guided) communication channel?
Answer: B
Coaxial cable, copper wire and optical fibre are guided media because the signal travels along a physical conductor or fibre; radio, microwave and satellite are wireless (unguided) media.
8.Which of the following is an example of a wireless (unguided) communication channel?
Answer: A
Microwave, radio wave and satellite links are wireless channels because the signal travels through free space (the atmosphere) without a physical conductor.
9.An optical fibre cable transmits signals using:
Answer: A
Optical fibres carry information as pulses of light that travel along the fibre core, kept inside by repeated total internal reflection at the core-cladding boundary.
10.Compared with an ordinary copper cable, an optical fibre cable generally offers:
Answer: A
Optical fibres can carry much more data (higher bandwidth) with less signal loss over long distances and are not affected by electromagnetic interference, unlike copper cables.
11.A coaxial cable is constructed with:
Answer: D
Coaxial cable has a central copper conductor, an insulating layer, a braided or foil metal shield, and an outer protective jacket, which reduces interference compared with plain copper wire.
12.Satellite communication relies mainly on:
Answer: C
In satellite communication, a ground station transmits a microwave signal up to an orbiting satellite, which amplifies it and relays it back down to another ground station, allowing communication over very long distances.
13.Microwave communication is commonly used for:
Answer: A
Microwaves travel in straight lines and are used for line-of-sight links such as mobile phone tower-to-tower links and satellite uplinks/downlinks.
14.Radio waves, microwaves and satellite links are all examples of wireless communication channels.
Answer: True
All three transmit signals through free space (the atmosphere or space) rather than along a physical conductor, so they are classed as wireless channels.
15.A communication channel that uses a physical conductor such as copper wire, coaxial cable, or optical fibre to carry a signal is called a ______ channel.
Answer: wired
Wired (guided) channels carry the signal along a physical medium, unlike wireless channels which use free space.
16.An analog signal is best described as one that:
Answer: B
An analog signal is a continuously varying quantity (such as voltage) that can take any value within a given range, changing smoothly over time.
17.A digital signal is best described as one that:
Answer: B
A digital signal is represented using discrete, distinct values (usually two levels corresponding to binary 0 and 1), changing abruptly between these levels rather than varying smoothly.
18.Which characteristic is typical of a digital signal but not of an analog signal?
Answer: D
Digital signals jump abruptly between a fixed set of discrete levels (usually two, representing binary 0 and 1), unlike analog signals which vary continuously.
19.One key advantage of digital signals over analog signals is that digital signals:
Answer: C
Digital signals can be easily distinguished from noise and regenerated (reshaped) at repeater stations, so they suffer far less quality loss than analog signals over distance or after copying.
20.Compared to digital signals, analog signals are generally:
Answer: B
Because analog signals vary continuously, noise added during transmission blends into the signal and is hard to remove, causing gradual degradation in quality, especially over long distances or after repeated amplification.
21.Digital signals are generally more resistant to noise than analog signals because their discrete levels can be clearly distinguished from noise and restored.
Answer: True
Since a digital signal only needs to be identified as one of a few fixed levels, small amounts of noise usually do not change which level is detected, allowing the original signal to be regenerated accurately.
22.An analog signal can only take two possible values at any instant in time.
Answer: False
An analog signal can take any value within a continuous range, unlike a digital signal, which is restricted to a limited number of discrete values (commonly two, for binary).
23.A signal that changes smoothly and continuously over time, able to take any value within a range, is called an ______ signal.
Answer: analog
This continuously varying type of signal is called an analog signal, in contrast to a digital signal, which uses discrete values.
24.A signal that is represented using a limited number of discrete values, most commonly two levels representing 0 and 1, is called a ______ signal.
Answer: digital
Such a signal uses fixed, distinct levels (binary digits) rather than varying continuously, and is called a digital signal.
25.In binary representation used in digital communication, information is encoded using:
Answer: D
Digital systems represent information using the binary number system, which has only two digits, 0 and 1, corresponding to two distinct voltage/signal levels.
26.Which of the following is an advantage of digital communication over analog communication?
Answer: A
Because digital information is represented as numbers (bits), computers can easily store, compress, encrypt, and apply error-detection and correction techniques to it, which is much harder to do reliably with analog signals.
27.A major disadvantage of analog signal transmission over long distances is that:
Answer: C
Every time an analog signal is amplified or relayed, the noise picked up along the way is amplified together with the wanted signal, so the quality steadily worsens with distance.
28.A telephone landline network historically using twisted-pair copper wires is an example of which type of communication channel?
Answer: C
Twisted-pair copper wire is a physical conductor along which the signal is guided, making it a wired communication channel.
29.Optical fibre cables can carry information over much longer distances with less signal loss than copper cables of similar length.
Answer: True
Light pulses in optical fibres experience far less attenuation (signal loss) than electrical signals in copper wires, allowing much longer transmission distances between repeaters.
30.Which of the following best explains why digital signals resist noise better than analog signals?
Answer: B
Because a digital receiver only needs to decide which of a few discrete levels (e.g. high/low) was sent, minor noise added during transmission is unlikely to push the signal past the threshold that would cause it to be misread.
31.Signal degradation refers to:
Answer: D
Signal degradation is the weakening or distortion of a signal (loss of quality or strength) as it travels along a transmission channel, often worsened by noise and attenuation.
32.Why can a digital signal be 'regenerated' (restored to its original clean form) at a repeater station more easily than an analog signal?
Answer: D
A repeater for a digital signal simply decides which discrete level (e.g. 0 or 1) was sent and outputs a fresh, clean version of that level, effectively removing accumulated noise; this is not possible for a continuously varying analog signal.
33.Which of these is NOT typically listed as an advantage of digital signals over analog signals?
Answer: D
Digital signals are praised for noise immunity, ease of processing/storage, and error correction — but equipment cost is not a defining advantage and can even be higher for digital systems.
34.A block diagram of a basic communication system is usually drawn in which order?
Answer: B
The standard order is Transmitter (sends the signal) → Channel (carries the signal) → Receiver (picks up the signal), representing the flow of the message from source to destination.
35.A device or system that converts a message signal so that it can be sent efficiently through a communication channel is called a ______.
Answer: transmitter
The transmitter's role is to prepare and send the message signal into the channel toward the receiver.
36.In everyday use, a mobile phone communicates with the network's base station mainly using which type of channel?
Answer: B
Mobile phones communicate with nearby base stations using wireless radio frequency (including microwave) signals, without needing a physical cable connection.
37.Household internet delivered through underground cables made of glass strands that carry pulses of light is an example of:
Answer: D
Fibre-optic internet uses thin glass or plastic strands to carry data as light pulses, making it a wired (guided) transmission channel.
38.A satellite communication system requires a signal to travel only along the ground between two fixed stations.
Answer: False
Satellite communication involves sending a signal up from a ground station to an orbiting satellite and then back down to another ground station, so the signal travels through space, not only along the ground.
39.Which statement correctly compares analog and digital signals?
Answer: A
Analog signals vary smoothly and continuously, while digital signals jump between a fixed set of discrete values, which is the fundamental distinction between the two.
40.A key reason modern telecommunication systems (such as mobile networks and the internet) have largely shifted from analog to digital technology is:
Answer: A
Digital technology allows signals to be compressed, encrypted, error-corrected, easily processed by computers, and multiplexed (many signals sharing one channel), all while resisting noise better than analog signals.
1.Electronics is best described as the branch of science and technology dealing with:
Answer: D
Electronics deals with circuits built from components like resistors, capacitors, diodes and transistors that control small electric currents to process, store or transmit information/signals.
2.Electronic components are generally divided into two broad categories, namely:
Answer: D
Electronic components are classified as passive (cannot amplify or control current on their own, e.g. resistors, capacitors, inductors) or active (can control/amplify current or voltage, e.g. diodes, transistors).
3.A passive electronic component is one that:
Answer: C
Passive components such as resistors, capacitors and inductors do not amplify signals or add energy to a circuit; they only store energy, dissipate it as heat, or oppose changes in current/voltage.
4.An active electronic component is one that:
Answer: D
Active components such as diodes and transistors can control, switch or amplify current or voltage, usually with the help of an external power supply.
5.Which of the following is classified as a passive electronic component?
Answer: B
Resistors, along with capacitors and inductors, are passive components; diodes, transistors and integrated circuits are active components.
6.Which of the following is classified as an active electronic component?
Answer: A
A transistor is an active component because it can amplify or switch electronic signals using an external power source; resistors, capacitors and inductors are passive.
7.The main function of a resistor in an electronic circuit is to:
Answer: A
A resistor's job is to resist (limit) the flow of current in a circuit, which is used to control current levels and to divide or drop voltage as needed.
8.The unit used to measure resistance is the:
Answer: D
Resistance is measured in ohms (Ω), named after Georg Ohm; the farad is used for capacitance and the henry for inductance.
9.A capacitor is a component that mainly:
Answer: B
A capacitor consists of two conducting plates separated by an insulating material (dielectric) and stores electrical energy in the electric field that forms between the plates when charged.
10.The unit used to measure capacitance is the:
Answer: C
Capacitance is measured in farads (F), commonly seen as microfarads (μF) or picofarads (pF) in practical circuits.
11.An inductor is a passive component that mainly:
Answer: A
An inductor is typically a coil of wire that stores energy in a magnetic field created as current flows through it, and it opposes changes in current.
12.The unit used to measure inductance is the:
Answer: B
Inductance is measured in henries (H), named after Joseph Henry.
13.Resistors, capacitors, and inductors are all classified as ______ electronic components because they do not amplify signals.
Answer: passive
These three components store or oppose energy/current but cannot amplify a signal on their own, so they are grouped as passive components.
14.Diodes and transistors are examples of ______ electronic components because they can control or amplify current using an external power source.
Answer: active
Active components, unlike passive ones, can control, switch, or amplify electrical signals with help from a power supply.
15.A diode is an active component that mainly:
Answer: A
A diode acts like a one-way valve for electric current: it conducts easily when forward biased and blocks current (ideally) when reverse biased, which is why diodes are used for rectification.
16.A common everyday application of a diode is:
Answer: C
Diodes are commonly used in rectifier circuits to convert AC mains supply into DC, which many electronic devices need to operate.
17.A light-emitting diode (LED) is a type of diode that:
Answer: D
An LED emits light when current flows through it in the forward direction, making it useful as an indicator light and in energy-efficient lighting.
18.A transistor is an active component mainly used to:
Answer: A
Transistors can amplify small input signals into larger output signals, or switch currents on and off, forming the basis of modern electronic amplifiers, computers, and digital logic circuits.
19.A basic bipolar transistor typically has how many terminals?
Answer: C
A standard bipolar junction transistor has three terminals: the base, the collector, and the emitter.
20.A resistor can amplify a weak electrical signal into a stronger one.
Answer: False
A resistor is a passive component; it can only limit or oppose current flow and dissipate energy as heat, but it cannot amplify a signal — amplification requires an active component such as a transistor.
21.A capacitor stores electrical energy in the form of an electric field between its plates.
Answer: True
When a capacitor is charged, opposite charges accumulate on its two plates, creating an electric field between them in which energy is stored.
22.On a typical computer motherboard, small cylindrical or disc-shaped components with coloured bands (or numbers) that limit current in various circuits are most likely:
Answer: B
Resistors are commonly seen on circuit boards as small components, often coded with colour bands or printed numbers, used to control current flow in different parts of the circuit.
23.On a motherboard, small cylindrical components (often with a polarity mark) that store charge and help smooth out voltage fluctuations are most likely:
Answer: D
Capacitors on motherboards are often seen as small cylindrical (electrolytic) or flat (ceramic) components, used to filter and smooth voltage supplied to other components.
24.The main integrated circuit (chip) on a motherboard, such as the central processing unit (CPU), is built up mainly from millions of tiny:
Answer: C
Modern integrated circuits like a CPU contain millions to billions of microscopic transistors that switch on and off to perform logical and arithmetic operations.
25.Which of the following is a real-life application that mainly relies on the switching/amplifying property of transistors?
Answer: C
Transistors are the building blocks of amplifiers (e.g., in phone/audio circuits) and digital logic gates (used inside computer processors), relying on their ability to amplify or switch current.
26.A component made of a coil of wire that stores energy in a magnetic field when current passes through it is called an ______.
Answer: inductor
An inductor stores magnetic energy and opposes sudden changes in current, and is typically constructed as a coil of wire.
27.Why are capacitors often used in power supply circuits of electronic devices?
Answer: A
Capacitors in power supplies charge up and discharge to smooth out ripples or fluctuations in the voltage, providing a steadier output to the rest of the circuit.
28.A photodiode used in devices such as remote-control receivers and light sensors works by:
Answer: C
A photodiode is a type of diode that responds to light, producing or changing an electric current when light strikes its junction, which is used in light-sensing applications.
29.A simple LED torch (flashlight) mainly demonstrates the everyday application of which type of electronic component?
Answer: B
An LED torch relies on light-emitting diodes, which convert electrical energy directly into visible light when forward biased, along with a resistor to limit current.
30.Solar (photovoltaic) cells, which convert light energy directly into electrical energy, are essentially a special type of:
Answer: C
A solar cell is a type of photodiode (a semiconductor diode) engineered to convert light energy efficiently into electrical energy through the photovoltaic effect.
31.Inductors and capacitors are both passive components, but they store energy in different forms: an inductor stores energy in a magnetic field while a capacitor stores energy in an electric field.
Answer: True
An inductor's energy is stored in the magnetic field around its coil due to current flow, whereas a capacitor's energy is stored in the electric field between its charged plates.
32.Which statement correctly distinguishes passive from active electronic components?
Answer: A
The key distinction is that active components (like transistors and diodes) can control or amplify current using an external energy source, while passive components (resistors, capacitors, inductors) cannot amplify signals and only store or oppose current.
33.A rectifier circuit found inside a phone charger mainly uses which type of component to convert AC into DC?
Answer: D
Diodes arranged in a rectifier circuit allow current to pass in only one direction, converting the alternating current from the mains supply into direct current suitable for charging a phone battery.
34.A variable resistor (potentiometer), such as the one used to control the volume of a radio, works by:
Answer: B
A potentiometer (variable resistor) allows the resistance in a circuit to be adjusted manually, which changes the current or voltage supplied to a component such as a speaker, adjusting the volume.
35.Which of the following best explains why transistors replaced older vacuum tubes in most electronic devices?
Answer: A
Transistors offered a smaller, more durable, more energy-efficient, and cheaper alternative to bulky, fragile, power-hungry vacuum tubes, which is why they became the standard active component in modern electronics.
36.A component that allows current to flow easily in one direction only, commonly used in rectifier circuits, is called a ______.
Answer: diode
A diode conducts in the forward direction and blocks current in the reverse direction, which makes it ideal for converting AC to DC in rectifier circuits.
37.A circuit that combines a resistor and a capacitor is often used in electronic devices to:
Answer: B
Resistor-capacitor (RC) combinations are widely used to create timing circuits (e.g., delays, oscillators) and filters that allow or block certain signal frequencies.
38.Which of these everyday devices relies heavily on basic electronic components such as resistors, capacitors, diodes and transistors working together?
Answer: B
A smartphone contains complex circuit boards packed with resistors, capacitors, diodes, transistors and integrated circuits working together to process signals, store data, and manage power.
39.On a motherboard, the small chips (integrated circuits) that combine many active and passive components into a single package are useful mainly because they:
Answer: D
Integrated circuits pack many transistors, resistors, diodes and other components onto a tiny silicon chip, enabling complex functions in a small, affordable, and reliable package.
40.A diode allows electric current to flow equally well in both the forward and reverse directions.
Answer: False
A diode is designed to conduct current easily in the forward direction only; in reverse bias it blocks (ideally stops) current flow, which is its defining property.