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 6 quiz.
1.Sound is produced by:
Answer: B
A vibrating source makes the particles of the medium vibrate.
2.Sound waves in air are:
Answer: A
Air particles vibrate parallel to the direction the wave travels, forming compressions and rarefactions.
3.Sound cannot travel through:
Answer: D
Sound needs a material medium; there are no particles in a vacuum.
4.In which medium does sound usually travel fastest?
Answer: D
Particles in solids are closely linked, so vibrations pass on quickly.
5.The speed of sound in air at room temperature is about:
Answer: D
About 343 m/s at 20 °C.
6.The speed of sound in air increases when:
Answer: C
Warmer air molecules move faster and pass on vibrations more quickly.
7.A sound wave has frequency 686 Hz in air (v = 343 m/s). What is its wavelength?
Answer: C
λ = v/f = 343 ÷ 686 = 0.5 m.
8.The pitch of a sound depends mainly on its:
Answer: C
Higher frequency gives a higher pitch.
9.The loudness of a sound depends mainly on its:
Answer: A
Larger amplitude vibrations carry more energy and sound louder.
10.Two instruments play the same note at the same loudness but sound different. This difference is called:
Answer: A
Different overtones (harmonics) give each instrument its own quality.
11.The normal range of human hearing is about:
Answer: C
Sounds above 20 kHz are ultrasound; below 20 Hz are infrasound.
12.Sound with frequency above 20 000 Hz is called:
Answer: A
Bats and medical scanners use ultrasound.
13.An echo is:
Answer: D
Echoes occur when sound reflects from a hard surface.
14.A girl shouts in front of a cliff and hears the echo 2.0 s later (v = 340 m/s). How far away is the cliff?
Answer: D
The sound travels there and back: d = vt/2 = 340 × 2 ÷ 2 = 340 m.
15.Sound bends around corners and through doorways because of:
Answer: B
Sound wavelengths are similar in size to doorways, so they diffract.
16.Beats are heard when:
Answer: C
The sounds interfere, making the loudness rise and fall.
17.Two tuning forks of 440 Hz and 444 Hz sound together. What is the beat frequency?
Answer: D
Beat frequency = 444 − 440 = 4 Hz.
18.On a string fixed at both ends, the fundamental (first harmonic) has a wavelength of:
Answer: B
The string length holds half a wavelength: λ = 2L.
19.A string 0.5 m long vibrates in its fundamental mode with wave speed 200 m/s. What is the fundamental frequency?
Answer: B
f = v/2L = 200 ÷ 1.0 = 200 Hz.
20.Increasing the tension of a guitar string makes its pitch:
Answer: A
Higher tension increases the wave speed and the frequency.
21.An open pipe (open at both ends) of length L has a fundamental wavelength of:
Answer: D
There is an antinode at each end, so λ = 2L.
22.A closed pipe (closed at one end) of length L has a fundamental wavelength of:
Answer: A
A node at the closed end and antinode at the open end hold a quarter wavelength: λ = 4L.
23.A pipe closed at one end produces only:
Answer: A
Only the 1st, 3rd, 5th… harmonics fit a closed pipe.
24.Resonance in sound occurs when:
Answer: C
Resonance tubes and musical instruments rely on it.
25.Sound intensity is defined as:
Answer: B
I = P/A, measured in W/m².
26.Sound intensity level is measured in:
Answer: B
β = 10 log(I/I₀) dB, with I₀ = 10⁻¹² W/m².
27.A sound has an intensity of 10⁻⁶ W/m². What is its intensity level? (I₀ = 10⁻¹² W/m²)
Answer: B
β = 10 log(10⁻⁶/10⁻¹²) = 10 log 10⁶ = 60 dB.
28.The Doppler effect is:
Answer: B
Example: a siren sounds higher as the ambulance approaches.
29.An ambulance siren sounds higher in pitch as it approaches you because:
Answer: A
Wavefronts bunch up in front of a moving source.
30.A source of frequency 500 Hz moves towards a stationary observer at 43 m/s (v = 343 m/s). What frequency is heard? (f' = f v/(v − vs))
Answer: C
f' = 500 × 343 ÷ (343 − 43) = 500 × 343/300 ≈ 572 Hz.
31.Sound can travel through a vacuum.
Answer: False
Sound needs a medium.
32.Sound waves in air are longitudinal waves.
Answer: True
Particles vibrate along the direction of travel.
33.A higher frequency gives a higher pitch.
Answer: True
Pitch depends on frequency.
34.Ultrasound has a frequency below 20 Hz.
Answer: False
Ultrasound is above 20 000 Hz; below 20 Hz is infrasound.
35.The pitch of a car horn sounds lower after the car has passed you.
Answer: True
As the source moves away, the received frequency drops.
36.Reflected sound that is heard after the original sound is called an ______.
Answer: echo
Used in echo sounding and sonar.
37.The unit of sound intensity level is the ______.
Answer: decibel (dB)
Named after Alexander Graham Bell.
38.The apparent change in frequency due to relative motion of source and observer is the ______ effect.
Answer: Doppler
Named after Christian Doppler.
39.The regions of high pressure in a sound wave are called ______.
Answer: compressions
Low-pressure regions are rarefactions.
40.Sound waves with frequencies above the range of human hearing are called ______.
Answer: ultrasound
Used in medical imaging.
1.Angular displacement is measured in:
Answer: C
One revolution = 2π rad.
2.Angular velocity ω is related to linear speed v at radius r by:
Answer: A
Points further from the axis move faster.
3.A wheel turns at 10 rad/s. What is the speed of a point 0.3 m from its axis?
Answer: B
v = ωr = 10 × 0.3 = 3 m/s.
4.Angular acceleration is:
Answer: A
α = Δω/Δt, measured in rad/s².
5.A fan speeds up from rest to 20 rad/s in 4 s. What is its angular acceleration?
Answer: B
α = 20 ÷ 4 = 5 rad/s².
6.Moment of inertia measures:
Answer: A
It is the rotational equivalent of mass.
7.The moment of inertia of a body depends on:
Answer: C
Mass further from the axis gives a larger moment of inertia.
8.The moment of inertia of a point mass m at distance r from an axis is:
Answer: A
I = mr², measured in kg m².
9.What is the moment of inertia of a 2 kg mass at 0.5 m from the axis?
Answer: D
I = mr² = 2 × 0.25 = 0.5 kg m².
10.Torque is:
Answer: D
τ = F × perpendicular distance, in N m.
11.A force of 20 N acts at right angles 0.4 m from a hinge. What is the torque?
Answer: A
τ = Fr = 20 × 0.4 = 8 N m.
12.Newton's second law for rotation is:
Answer: C
Torque = moment of inertia × angular acceleration.
13.A torque of 12 N m acts on a wheel with I = 3 kg m². What is its angular acceleration?
Answer: C
α = τ/I = 12 ÷ 3 = 4 rad/s².
14.Rotational kinetic energy is given by:
Answer: A
KE_rot = ½Iω².
15.A flywheel with I = 4 kg m² spins at 5 rad/s. What is its rotational kinetic energy?
Answer: C
KE = ½ × 4 × 5² = 50 J.
16.Angular momentum L of a rotating body is:
Answer: C
L = Iω, measured in kg m²/s.
17.The law of conservation of angular momentum states that, with no external torque:
Answer: D
Iω = constant.
18.An ice skater spinning with arms out pulls her arms in. She spins faster because:
Answer: D
This is conservation of angular momentum.
19.A diver tucks into a ball during a dive in order to:
Answer: B
Smaller I gives larger ω for the same angular momentum.
20.Power in rotational motion is given by:
Answer: B
Power = torque × angular velocity.
21.A motor provides a torque of 5 N m at 100 rad/s. What is its power?
Answer: A
P = τω = 5 × 100 = 500 W.
22.Work done by a constant torque τ turning a body through angle θ is:
Answer: B
W = τθ (θ in radians).
23.A body is in rotational equilibrium when:
Answer: D
Clockwise and anticlockwise moments balance.
24.A rolling ball has kinetic energy that is:
Answer: A
It moves forward and spins at the same time.
25.A solid cylinder and a hollow cylinder of the same mass and radius roll down a slope. Which reaches the bottom first?
Answer: D
The solid cylinder has a smaller moment of inertia, so less energy goes into spinning.
26.A wheel makes 120 revolutions per minute. What is its angular velocity?
Answer: B
f = 2 rev/s; ω = 2πf = 4π ≈ 12.6 rad/s.
27.Flywheels are used in engines to:
Answer: B
Their large moment of inertia resists changes in speed.
28.The SI unit of angular momentum is:
Answer: B
L = Iω: kg m² × rad/s.
29.A door handle is placed far from the hinges so that:
Answer: C
Torque = force × distance from the axis.
30.A 0.2 kg stone is whirled on a 0.5 m string at 4 rad/s. What is its angular momentum?
Answer: D
I = mr² = 0.2 × 0.25 = 0.05 kg m²; L = Iω = 0.05 × 4 = 0.2 kg m²/s.
31.Moment of inertia depends on how mass is distributed about the axis.
Answer: True
Mass far from the axis increases I.
32.Torque is the rotational equivalent of force.
Answer: True
τ = Iα mirrors F = ma.
33.If no external torque acts, angular momentum is conserved.
Answer: True
Iω stays constant.
34.A spinning skater slows down when she pulls her arms in.
Answer: False
She speeds up, because her moment of inertia decreases.
35.Rotational kinetic energy is ½Iω².
Answer: True
The rotational form of ½mv².
36.The turning effect of a force is called ______.
Answer: torque (moment)
τ = F × r.
37.The rotational equivalent of mass is the moment of ______.
Answer: inertia
I = Σmr².
38.Angular momentum L = I × ______.
Answer: ω (angular velocity, w)
L = Iω.
39.The SI unit of angular velocity is the ______ per second.
Answer: radian
rad/s.
40.Newton's second law for rotation is τ = I × ______.
Answer: α (angular acceleration, a)
τ = Iα.
1.Faraday's law of electromagnetic induction relates induced EMF to:
Answer: A
Faraday's law states that the induced EMF equals the negative rate of change of magnetic flux linkage: EMF = -dΦ/dt.
2.Lenz's law states that the direction of induced current is such that it:
Answer: A
Lenz's law: the induced current flows in a direction that opposes the change in flux that caused it, consistent with conservation of energy.
3.Motional EMF is induced when:
Answer: A
A conductor moving through a magnetic field, cutting through field lines, induces a motional EMF given by EMF = BLv (for motion perpendicular to B and the conductor).
4.The formula for motional EMF of a rod of length L moving with velocity v perpendicular to field B is:
Answer: B
Motional EMF for a straight conductor moving perpendicular to both its length and a uniform field is EMF = BLv.
5.Self-inductance of a coil is defined by the relation:
Answer: B
Self-induced EMF is given by EMF = -L(dI/dt), where L is the self-inductance of the coil.
6.The SI unit of inductance is the:
Answer: C
Inductance is measured in henries (H).
7.Mutual inductance describes:
Answer: D
Mutual inductance is the EMF induced in one coil due to a changing current in a neighbouring coil, the basis of transformer operation.
8.A transformer works on the principle of:
Answer: B
A transformer transfers energy between coils via mutual induction, using a shared magnetic core to link the changing flux.
9.For an ideal transformer, the turns ratio relates voltages as:
Answer: B
For an ideal transformer, V1/V2 = N1/N2, where V1, V2 are primary/secondary voltages and N1, N2 are the corresponding turns.
10.A step-up transformer:
Answer: C
A step-up transformer has more secondary turns than primary, increasing voltage while decreasing current (conserving power, ideally).
11.Eddy currents are induced circulating currents that:
Answer: C
Eddy currents are loops of induced current in bulk conducting material due to changing flux, generally causing unwanted heating and energy loss.
12.Laminating the iron core of a transformer helps to:
Answer: D
Laminating the core into thin insulated sheets increases resistance to eddy current loops, reducing associated energy losses.
13.An AC generator converts:
Answer: A
A generator (alternator/dynamo) converts mechanical energy (rotation) into electrical energy via electromagnetic induction.
14.The induced EMF in a rotating coil generator is maximum when the coil plane is:
Answer: D
EMF is maximum when the rate of change of flux is greatest, which occurs when the coil plane is parallel to the field (flux through the coil is momentarily zero but changing fastest).
15.Increasing the speed of rotation of a generator coil ___ the induced EMF.
Answer: D
Since EMF depends on the rate of change of flux, increasing rotational speed increases the induced EMF.
16.A coil of N turns experiences a changing flux of dΦ/dt. The induced EMF is:
Answer: B
For a coil of N turns, the total induced EMF is N times the rate of change of flux through a single turn: EMF = N(dΦ/dt).
17.Lenz's law is a consequence of the conservation of:
Answer: B
Lenz's law ensures that induced currents oppose the change causing them, consistent with the conservation of energy (otherwise energy could be created from nothing).
18.A magnet moving towards a coil induces a current that creates a magnetic field which:
Answer: C
By Lenz's law, the induced current opposes the change (the approaching magnet), creating a field that repels the magnet, resisting its motion.
19.Transformers only work with:
Answer: B
Transformers require a changing magnetic flux, so they only function with alternating current, not steady DC.
20.The efficiency of a real transformer is reduced mainly due to:
Answer: B
Real transformers lose some energy to resistance in the windings (copper losses) and eddy currents/hysteresis in the core (iron losses).
21.A rod of length 0.5 m moves at 4 m/s perpendicular to a 0.2 T field. The induced EMF is:
Answer: A
EMF = BLv = 0.2 × 0.5 × 4 = 0.4 V.
22.If the number of turns in the secondary coil of a transformer is greater than the primary, the transformer:
Answer: A
More secondary turns than primary turns results in a higher output voltage than input — a step-up transformer.
23.The induced current opposing an increasing flux through a coil will flow in a direction to:
Answer: C
According to Lenz's law, the induced current creates a magnetic field that opposes the increasing flux, i.e. acts to reduce the rate of increase.
24.A generator's EMF output can be increased by:
Answer: D
EMF can be increased by rotating the coil faster, using more turns, or using a stronger magnetic field — all increase the rate of flux change.
25.A step-down transformer is commonly used in household appliance adaptors to:
Answer: A
Step-down transformers reduce high mains voltage to the lower voltage required by many household electronic devices.
26.Mutual inductance between two coils depends on:
Answer: A
Mutual inductance depends on the physical arrangement, number of turns, and how well the magnetic flux links the two coils.
27.A changing electric field can also induce a magnetic field, according to:
Answer: D
Maxwell showed that a changing electric field also produces a magnetic field, extending Ampere's law and unifying electromagnetism.
28.Induction cookers work by using:
Answer: C
Induction cookers use a coil producing a changing magnetic field, which induces eddy currents in a ferromagnetic pan, heating it directly.
29.The unit of magnetic flux, the weber, is equivalent to:
Answer: C
One weber equals one volt-second (Wb = V·s), consistent with EMF = -dΦ/dt.
30.A bicycle dynamo generates electricity by:
Answer: D
A bicycle dynamo uses the wheel's rotation to spin a magnet near a coil, inducing an EMF via electromagnetic induction.
31.Lenz's law is essentially a statement of the conservation of energy.
Answer: True
Since induced effects always oppose the change that causes them, energy must be supplied to maintain that change, consistent with conservation of energy.
32.A stationary coil in a stationary magnetic field will have an induced EMF.
Answer: False
Since there is no change in flux (nothing moving, nothing changing), no EMF is induced in a stationary coil in a static field.
33.Transformers can step up or step down both AC and DC voltages equally well.
Answer: False
Transformers rely on changing flux and work only with AC; they do not function to transform steady DC voltages.
34.Eddy currents are generally undesirable in transformer cores because they cause energy loss as heat.
Answer: True
Eddy currents circulating in the core dissipate energy as heat, reducing transformer efficiency, so they are minimized using laminated cores.
35.The induced EMF in a coil depends only on the number of turns, not on the rate of change of flux.
Answer: False
Induced EMF depends on both the number of turns and the rate of change of flux: EMF = N(dΦ/dt).
36.The law stating that induced EMF equals the rate of change of flux is ______'s law.
Answer: Faraday
Faraday's law of electromagnetic induction: EMF = -N(dΦ/dt).
37.The law that gives the direction of induced current, opposing the change producing it, is ______'s law.
Answer: Lenz
Lenz's law gives the direction of induced current, always opposing the change in flux.
38.The property of a coil that opposes changes in its own current is called ______-inductance.
Answer: self
Self-inductance is the property by which a changing current in a coil induces an opposing EMF in itself.
39.A device that transfers electrical energy between two coils via a shared changing magnetic flux is called a ______.
Answer: transformer
A transformer uses mutual induction between primary and secondary coils to transfer and transform AC voltage/current.
40.Unwanted circulating currents induced in bulk conductors due to changing flux are called ______ currents.
Answer: eddy
Eddy currents are induced loops of current in conducting material, often causing unwanted heating.
1.An alternating current is one that:
Answer: C
Alternating current periodically changes direction and magnitude, typically following a sinusoidal pattern.
2.The root-mean-square (rms) value of an AC voltage relates to peak voltage V0 by:
Answer: D
For a sinusoidal AC signal, Vrms = V0/√2 ≈ 0.707 V0.
3.The rms value of AC is significant because it represents:
Answer: B
The rms value represents the equivalent DC value that would produce the same average power dissipation in a resistor.
4.The frequency of standard mains AC supply is commonly:
Answer: A
Mains AC frequency is typically 50 Hz (many countries including Rwanda) or 60 Hz (e.g., USA).
5.In a purely resistive AC circuit, current and voltage are:
Answer: B
In a purely resistive circuit, current and voltage reach their maximum and zero values simultaneously — they are in phase.
6.In a purely capacitive AC circuit, the current:
Answer: C
In a purely capacitive circuit, current leads voltage by 90° (a common memory aid is 'ICE': in a Capacitor, I leads E).
7.In a purely inductive AC circuit, the current:
Answer: C
In a purely inductive circuit, current lags voltage by 90° ('ELI': in an inductor L, E leads I).
8.Capacitive reactance is given by:
Answer: D
Capacitive reactance Xc = 1/(2πfC), which decreases as frequency increases.
9.Inductive reactance is given by:
Answer: B
Inductive reactance XL = 2πfL, which increases as frequency increases.
10.As frequency increases, capacitive reactance:
Answer: A
Since Xc = 1/(2πfC), reactance decreases as frequency increases — capacitors pass higher frequencies more easily.
11.As frequency increases, inductive reactance:
Answer: D
Since XL = 2πfL, reactance increases with frequency — inductors oppose higher frequencies more strongly.
12.Impedance in an AC circuit is the:
Answer: A
Impedance Z is the total opposition to AC current flow, combining both resistance and reactance (Z = √(R² + X²) for series RLC).
13.Resonance in a series LCR circuit occurs when:
Answer: D
Resonance occurs when inductive and capacitive reactances are equal (XL = Xc), making impedance purely resistive and minimum.
14.At resonance in a series LCR circuit, the impedance is:
Answer: C
At resonance, XL and Xc cancel, leaving only resistance R, which is the minimum possible impedance for that circuit.
15.The resonant frequency of a series LCR circuit is given by:
Answer: B
The resonant frequency is f0 = 1/(2π√(LC)), derived by setting XL = Xc.
16.Average power in a purely resistive AC circuit is given by:
Answer: B
Average power dissipated in a resistive AC circuit is P = VrmsIrms (= Irms²R = Vrms²/R).
17.The average power delivered in a purely reactive (inductive or capacitive) AC circuit is:
Answer: D
In a purely reactive circuit, current and voltage are 90° out of phase, so the average power delivered over a cycle is zero.
18.Power factor in an AC circuit is defined as:
Answer: A
Power factor = cosθ, where θ is the phase difference between voltage and current; it indicates the effectiveness of power delivery.
19.A capacitor connected across an AC supply allows current to flow because:
Answer: D
Although no charge crosses the gap between plates, the continuous charging and discharging as AC voltage alternates results in an effective AC current flow.
20.An AC voltage of peak value 340 V has an rms value of approximately:
Answer: C
Vrms = V0/√2 = 340/1.414 ≈ 240 V, a typical mains rms voltage.
21.Which quantity remains constant regardless of frequency in an AC circuit containing only a resistor?
Answer: A
A pure resistor's resistance R does not depend on frequency, unlike reactance which changes with frequency in capacitors and inductors.
22.The phase angle between current and voltage in a series LCR circuit at resonance is:
Answer: C
At resonance, the circuit behaves purely resistively, so current and voltage are in phase (phase angle = 0°).
23.A transformer is more efficient with AC than DC because:
Answer: A
Only a changing current (as in AC) produces a continuously changing magnetic flux, which is required for transformer operation via mutual induction.
24.At very low frequency, a capacitor in an AC circuit behaves almost like:
Answer: B
Since Xc = 1/(2πfC), as frequency approaches zero, reactance becomes very large, so the capacitor behaves almost like an open circuit (as with DC).
25.At very high frequency, an inductor in an AC circuit behaves almost like:
Answer: B
Since XL = 2πfL, as frequency increases, reactance becomes very large, so the inductor behaves almost like an open circuit at high frequency.
26.Household electricity meters usually measure energy consumption in:
Answer: A
Electrical energy consumption for billing is typically measured in kilowatt-hours (kWh).
27.A step-up transformer used to transmit electricity over long distances helps by:
Answer: B
Stepping up voltage for transmission reduces the current needed for a given power, which reduces I²R losses in transmission lines.
28.Quality factor (Q) of a resonant LCR circuit indicates:
Answer: D
The Q factor describes how sharp and narrow the resonance peak is — higher Q means a more selective (narrower bandwidth) resonant circuit.
29.A rectifier is used to convert:
Answer: A
A rectifier circuit (using diodes) converts alternating current into direct current.
30.An oscilloscope displaying an AC signal typically shows:
Answer: C
An oscilloscope displays the AC voltage as a sinusoidal waveform, showing how it varies periodically with time.
31.The average value of a pure sine wave AC voltage over a complete cycle is zero.
Answer: True
Since the positive and negative halves of a sine wave are symmetric, their average over a full cycle is exactly zero.
32.In a purely resistive AC circuit, no phase difference exists between voltage and current.
Answer: True
Resistors do not introduce any phase shift, so voltage and current remain in phase in a purely resistive AC circuit.
33.At resonance, a series LCR circuit has maximum impedance.
Answer: False
At resonance, impedance is minimum (equal to R alone), not maximum, since the reactances cancel.
34.Inductive reactance decreases with increasing frequency.
Answer: False
Inductive reactance XL = 2πfL increases with frequency, the opposite of capacitive reactance.
35.Power factor of 1 indicates that voltage and current are perfectly in phase.
Answer: True
A power factor of cosθ = 1 means θ = 0°, so voltage and current are exactly in phase, giving maximum real power transfer.
36.The rms value of a sinusoidal peak voltage V0 is Vrms = V0/______.
Answer: √2
Vrms = V0/√2 for a sinusoidal AC waveform.
37.The opposition offered by a capacitor to AC current is called capacitive ______.
Answer: reactance
Capacitive reactance Xc = 1/(2πfC) is the opposition a capacitor offers to alternating current.
38.The condition XL = Xc in a series LCR circuit defines the point of ______.
Answer: resonance
Resonance occurs precisely when inductive and capacitive reactances are equal in magnitude.
39.The total opposition to current flow in an AC circuit, combining resistance and reactance, is called ______.
Answer: impedance
Impedance (Z) is the combined opposition to AC current from both resistance and reactance.
40.cosθ, the ratio that indicates how effectively power is delivered in an AC circuit, is called the ______ factor.
Answer: power
The power factor, cosθ, indicates the phase relationship between voltage and current and how effectively real power is delivered.
1.The nucleus of an atom is composed of:
Answer: D
The atomic nucleus contains protons (positively charged) and neutrons (neutral), collectively called nucleons.
2.Isotopes of an element have:
Answer: D
Isotopes share the same atomic number (same number of protons) but differ in neutron number, giving different mass numbers.
3.Alpha decay involves the emission of:
Answer: D
Alpha particles are helium nuclei consisting of 2 protons and 2 neutrons, emitted during alpha decay.
4.Beta-minus decay involves the emission of:
Answer: C
In beta-minus decay, a neutron in the nucleus converts into a proton, emitting an electron and an antineutrino.
5.Gamma decay involves the emission of:
Answer: B
Gamma decay is the emission of high-energy electromagnetic radiation (photons) as a nucleus transitions from an excited to a lower energy state.
6.The half-life of a radioactive isotope is defined as:
Answer: B
Half-life is the time required for half of the radioactive nuclei present in a sample to undergo decay.
7.The radioactive decay law is expressed as:
Answer: A
The number of undecayed nuclei follows exponential decay: N = N0e^(-λt), where λ is the decay constant.
8.The decay constant λ is related to half-life T½ by:
Answer: C
The relationship between decay constant and half-life is λ = ln2/T½ (approximately 0.693/T½).
9.Activity of a radioactive sample is defined as:
Answer: B
Activity A = λN, the rate at which radioactive decays occur in a sample, usually measured in becquerels (Bq).
10.The SI unit of radioactive activity is the:
Answer: D
The becquerel (Bq) is the SI unit of radioactivity, equal to one decay per second.
11.Which type of radiation has the greatest penetrating power?
Answer: B
Gamma rays are electromagnetic radiation with the highest penetrating power, able to pass through several centimetres of lead, unlike alpha or beta particles.
12.Alpha particles can typically be stopped by:
Answer: B
Alpha particles have low penetrating power and can be stopped by just a sheet of paper or a few centimetres of air.
13.Mass defect in a nucleus refers to:
Answer: D
Mass defect is the small difference between the total mass of separate nucleons and the actual (lower) mass of the bound nucleus, converted to binding energy.
14.According to Einstein's mass-energy relation, energy equivalent to mass m is given by:
Answer: A
Einstein's famous equation E = mc² relates mass and energy, where c is the speed of light.
15.Binding energy of a nucleus represents:
Answer: B
Binding energy is the energy equivalent of the mass defect, representing the energy needed to separate a nucleus into its individual nucleons (or released when it forms).
16.Nuclear fission is a process in which:
Answer: A
Nuclear fission involves a heavy nucleus (like uranium-235) splitting into two lighter nuclei, releasing significant energy and often more neutrons.
17.Nuclear fusion is a process in which:
Answer: A
Nuclear fusion involves light nuclei (like hydrogen isotopes) combining to form a heavier nucleus, releasing large amounts of energy — the process powering stars.
18.Nuclear fusion powers:
Answer: A
Stars, including the Sun, are powered primarily by nuclear fusion, mainly converting hydrogen into helium.
19.A chain reaction in nuclear fission occurs when:
Answer: D
In a chain reaction, neutrons released by one fission event go on to trigger further fission events in neighbouring nuclei, sustaining the reaction.
20.Nuclear power stations typically use fission of which element?
Answer: A
Nuclear power stations commonly use uranium-235 (or plutonium) as fuel for controlled fission reactions to generate heat and electricity.
21.A control rod in a nuclear reactor is used to:
Answer: D
Control rods, often made of materials like boron or cadmium, absorb neutrons to regulate and control the rate of the fission chain reaction.
22.Ionizing radiation can be harmful to living tissue mainly because it:
Answer: B
Ionizing radiation can damage biological molecules, including DNA, potentially causing cell damage or mutations, which is why radiation exposure must be carefully controlled.
23.Radioactive dating (e.g., carbon-14 dating) relies on:
Answer: B
Radiometric dating uses the known, constant half-life of a radioactive isotope (like carbon-14) to estimate the age of a sample based on how much has decayed.
24.A sample with a half-life of 10 years will have what fraction remaining after 20 years?
Answer: A
After 20 years (2 half-lives), the remaining fraction is (1/2)² = 1/4.
25.The atomic number Z of a nucleus represents:
Answer: C
Atomic number Z is the number of protons in the nucleus, which determines the element's identity.
26.The mass number A of a nucleus represents:
Answer: C
Mass number A = number of protons + number of neutrons (total nucleons) in the nucleus.
27.In beta-plus (positron) decay, a proton in the nucleus converts into:
Answer: C
In beta-plus decay, a proton converts into a neutron, emitting a positron (positive electron) and a neutrino.
28.Radioactive decay is a random process, meaning:
Answer: C
While the exact decay time of any single nucleus is random and unpredictable, the statistical behaviour of a large collection of nuclei follows a predictable exponential decay law.
29.Which safety precaution is commonly used to protect against radioactive exposure?
Answer: A
The standard principles for radiation safety are minimizing time of exposure, maximizing distance from the source, and using appropriate shielding.
30.The energy released in nuclear fission/fusion reactions comes primarily from:
Answer: C
The enormous energy from nuclear reactions arises because a small amount of mass is converted directly into energy, as described by E = mc².
31.Isotopes of the same element have identical chemical properties but different atomic masses.
Answer: True
Since isotopes have the same number of protons (and electrons), their chemical properties are essentially identical, but differing neutron numbers give different atomic masses.
32.Gamma rays are the least penetrating type of nuclear radiation.
Answer: False
Gamma rays are the most penetrating type of the three main types of nuclear radiation (alpha, beta, gamma).
33.Nuclear fusion releases energy by combining light nuclei into a heavier nucleus.
Answer: True
Fusion combines light nuclei (e.g., hydrogen isotopes) into a heavier nucleus, releasing energy in the process.
34.The half-life of a radioactive isotope changes with temperature and pressure.
Answer: False
Half-life is a nuclear property that is essentially constant, unaffected by external conditions like temperature, pressure, or chemical state.
35.A chain reaction in nuclear fission requires the release of neutrons that trigger subsequent fission events.
Answer: True
Sustained chain reactions rely on neutrons released from each fission event going on to cause further fission in neighbouring nuclei.
36.The time taken for half of the radioactive nuclei in a sample to decay is called the ______.
Answer: half-life
Half-life is the characteristic time for half of a radioactive sample's nuclei to decay.
37.The SI unit of radioactive activity is the ______.
Answer: becquerel
Activity, the rate of nuclear decay, is measured in becquerels (Bq), equal to one decay per second.
38.The process in which a heavy nucleus splits into two lighter nuclei is called nuclear ______.
Answer: fission
Nuclear fission is the splitting of a heavy nucleus into two (or more) lighter nuclei, releasing energy.
39.The process in which light nuclei combine to form a heavier nucleus is called nuclear ______.
Answer: fusion
Nuclear fusion is the combination of light nuclei into a heavier nucleus, the process that powers stars.
40.The energy released when nucleons bind together to form a nucleus is called the ______ energy.
Answer: binding
Binding energy is the energy released (equivalent to the mass defect) when separate nucleons combine into a bound nucleus.
1.An elementary (fundamental) particle is one that:
Answer: D
Quarks and leptons are thought to be elementary.
2.Protons and neutrons are made of:
Answer: C
Each contains three quarks.
3.A proton is made of:
Answer: C
uud: charges +2/3 + 2/3 − 1/3 = +1.
4.A neutron is made of:
Answer: A
udd: +2/3 − 1/3 − 1/3 = 0.
5.The charge of an up quark is:
Answer: C
Up quarks carry +2/3 e; down quarks carry −1/3 e.
6.Which of these is a lepton?
Answer: D
Leptons include electrons, muons, taus and neutrinos.
7.Particles made of quarks are called:
Answer: B
Hadrons include baryons (three quarks) and mesons (quark–antiquark).
8.A baryon is made of:
Answer: B
Protons and neutrons are baryons.
9.A meson is made of:
Answer: A
Pions and kaons are mesons.
10.The antiparticle of the electron is the:
Answer: B
The positron has the same mass but positive charge.
11.When a particle meets its antiparticle, they:
Answer: D
Their mass is converted to energy, E = mc².
12.An antiparticle has the same mass as its particle but:
Answer: A
Other quantum numbers are also opposite.
13.The four fundamental interactions are:
Answer: A
All forces in nature come from these four.
14.The strongest of the four fundamental interactions is the:
Answer: B
It holds quarks and nucleons together.
15.The weakest of the four fundamental interactions is:
Answer: D
Gravity is very weak but acts over huge distances.
16.The interaction responsible for beta decay is the:
Answer: A
The weak force changes one quark flavour into another.
17.The strong nuclear force acts:
Answer: A
Its range is about 10⁻¹⁵ m.
18.The particle that carries the electromagnetic force is the:
Answer: B
Charged particles exchange photons.
19.The particle that carries the strong force between quarks is the:
Answer: C
Gluons 'glue' quarks together.
20.The weak interaction is carried by:
Answer: C
These are heavy exchange particles.
21.Which quantity is conserved in all particle reactions?
Answer: C
Charge, energy, momentum and baryon and lepton numbers are conserved.
22.The baryon number of a proton is:
Answer: D
Each quark has baryon number +1/3; three quarks give +1.
23.The lepton number of an electron is:
Answer: B
Leptons have L = +1; antileptons have L = −1.
24.In beta-minus decay, a neutron changes into:
Answer: C
n → p + e⁻ + ν̄; charge and lepton number are conserved.
25.Neutrinos are hard to detect because they:
Answer: D
Billions pass through your body every second.
26.Particle accelerators are used to:
Answer: A
Collisions reveal new particles.
27.Positrons are used in medicine in:
Answer: B
Annihilation gamma rays reveal where a tracer collects.
28.Matter is made of atoms; atoms contain a nucleus and:
Answer: D
Electrons surround the nucleus of protons and neutrons.
29.The total charge of a meson made of an up quark and an anti-down quark is:
Answer: B
u (+2/3) + anti-d (+1/3) = +1 (this is the π⁺).
30.Which conservation law rules out the decay p → e⁺ + γ?
Answer: A
Baryon number changes from +1 to 0, so the decay is forbidden.
31.Electrons are made of quarks.
Answer: False
Electrons are leptons and are elementary.
32.A positron is the antiparticle of the electron.
Answer: True
Same mass, opposite charge.
33.Gravity is the strongest of the four fundamental interactions.
Answer: False
Gravity is the weakest; the strong force is the strongest.
34.Electric charge is conserved in all particle reactions.
Answer: True
Total charge before = total charge after.
35.Protons and neutrons are hadrons.
Answer: True
They are made of quarks.
36.Particles such as the electron and neutrino belong to the group called ______.
Answer: leptons
They do not feel the strong force.
37.The particles that make up protons and neutrons are called ______.
Answer: quarks
Up and down quarks.
38.When a particle and its antiparticle meet and turn into energy, the process is called ______.
Answer: annihilation
Usually producing gamma photons.
39.The force that holds quarks together inside protons and neutrons is the ______ force.
Answer: strong (nuclear)
Carried by gluons.
40.The exchange particle of the electromagnetic force is the ______.
Answer: photon
A quantum of light.
1.X-rays are:
Answer: D
Their wavelengths are about 10⁻¹¹ to 10⁻⁸ m.
2.X-rays were discovered in 1895 by:
Answer: D
Röntgen noticed a glow from a cathode-ray tube.
3.In an X-ray tube, X-rays are produced when:
Answer: C
The electrons decelerate suddenly and emit X-ray photons.
4.Electrons in an X-ray tube are produced by:
Answer: D
Heating the filament releases electrons.
5.The metal target in an X-ray tube is usually made of tungsten because tungsten:
Answer: A
Most of the electrons' energy becomes heat, so the target must withstand high temperatures.
6.Most of the energy of the electrons hitting an X-ray target is converted to:
Answer: D
Only about 1 % becomes X-rays.
7.Increasing the accelerating voltage of an X-ray tube produces X-rays that are:
Answer: A
Higher-energy electrons produce higher-energy photons.
8.Increasing the filament current in an X-ray tube increases the:
Answer: D
More electrons hit the target per second.
9.The maximum energy of an X-ray photon from a tube operating at 30 kV is:
Answer: B
An electron accelerated through 30 kV gains 30 keV.
10.X-rays are used to show broken bones because:
Answer: D
Bones appear white on the image where fewer X-rays reach the detector.
11.At airports, X-rays are used to:
Answer: A
Different materials absorb X-rays differently.
12.A danger of X-rays is that they:
Answer: A
Exposure must be kept as low as possible.
13.Radiographers stand behind lead screens because lead:
Answer: B
Lead's high density and atomic number stop X-rays.
14.LASER stands for:
Answer: A
The key process is stimulated emission.
15.Stimulated emission occurs when:
Answer: C
The new photon has the same frequency, phase and direction.
16.Spontaneous emission happens when:
Answer: D
Ordinary lamps produce light this way.
17.Population inversion in a laser means:
Answer: B
This is needed for stimulated emission to dominate.
18.The process of supplying energy to the laser medium to create population inversion is called:
Answer: B
Pumping can be done with light, electricity or chemical reactions.
19.The two mirrors at the ends of a laser tube:
Answer: B
One mirror is fully reflecting, the other partly transmitting.
20.Laser light is monochromatic, meaning it:
Answer: C
All photons have the same frequency.
21.Laser light is coherent, meaning its waves:
Answer: C
Coherence allows interference and holography.
22.A laser beam stays narrow over long distances because laser light is:
Answer: C
Laser beams spread very little.
23.Which is a medical use of lasers?
Answer: A
Lasers reshape the cornea precisely.
24.Barcode scanners in shops use:
Answer: B
The laser is reflected from the black and white bars.
25.Optical fibre communication uses laser light because laser light:
Answer: C
Pulses of laser light carry data.
26.A danger of laser light is that it can:
Answer: A
Never look directly into a laser beam.
27.Compared with visible light, X-rays have:
Answer: C
X-rays are more energetic.
28.A photon of X-rays has energy 1.6 × 10⁻¹⁵ J. Its energy in electronvolts is: (1 eV = 1.6 × 10⁻¹⁹ J)
Answer: B
1.6 × 10⁻¹⁵ ÷ 1.6 × 10⁻¹⁹ = 10⁴ eV = 10 keV.
29.Lasers are used in industry for:
Answer: A
Focused laser beams deliver very high power to a small spot.
30.A CT scanner differs from an ordinary X-ray because it:
Answer: B
A computer combines the images into slices.
31.X-rays are a form of electromagnetic radiation.
Answer: True
They travel at the speed of light.
32.Laser light contains many different wavelengths.
Answer: False
Laser light is monochromatic.
33.X-rays can pass easily through lead.
Answer: False
Lead absorbs X-rays strongly.
34.Stimulated emission produces photons identical to the stimulating photon.
Answer: True
Same frequency, phase and direction.
35.It is safe to look directly into a laser beam.
Answer: False
It can damage the eye permanently.
36.In LASER, the letter S stands for ______.
Answer: stimulated
Light Amplification by Stimulated Emission of Radiation.
37.The metal often used as the target in an X-ray tube is ______.
Answer: tungsten
It has a very high melting point.
38.Laser light that has a single wavelength is described as ______.
Answer: monochromatic
Mono means one, chroma means colour.
39.Having more atoms in an excited state than in a lower state is called population ______.
Answer: inversion
Needed for laser action.
40.Electrons are released from the hot filament of an X-ray tube by ______ emission.
Answer: thermionic
Heat gives electrons enough energy to escape.
1.Ionising radiation is radiation that:
Answer: A
Examples: X-rays, gamma rays, alpha and beta particles.
2.Which of these is NOT ionising radiation?
Answer: A
Radio waves have too little energy per photon to ionise atoms.
3.Which radiation is the most strongly ionising?
Answer: C
Alpha particles are heavy and doubly charged, so they ionise strongly but travel only short distances.
4.When radiation passes through matter, its intensity:
Answer: C
Radiation is absorbed and scattered.
5.The absorbed dose of radiation is:
Answer: D
D = E/m.
6.The unit of absorbed dose is the:
Answer: B
1 Gy = 1 J/kg.
7.A 50 kg patient absorbs 0.1 J of energy from X-rays. What is the absorbed dose?
Answer: C
D = E/m = 0.1 ÷ 50 = 0.002 Gy (2 mGy).
8.The equivalent dose takes into account:
Answer: A
Equivalent dose = absorbed dose × radiation weighting factor.
9.The unit of equivalent dose is the:
Answer: A
It measures biological effect.
10.Alpha radiation has a weighting factor of 20 and X-rays a factor of 1. For the same absorbed dose, alpha radiation is:
Answer: B
Equivalent dose = D × w_R.
11.A worker receives an absorbed dose of 0.01 Gy of alpha radiation (w_R = 20). What is the equivalent dose?
Answer: C
H = 0.01 × 20 = 0.2 Sv.
12.Background radiation comes from:
Answer: B
It is always present at a low level.
13.The three main ways to reduce exposure to radiation are:
Answer: C
Spend less time, keep further away and use shielding.
14.Radiation workers wear a film badge or dosimeter to:
Answer: D
Doses are recorded to keep them below safe limits.
15.The ALARA principle in radiation safety means keeping doses:
Answer: A
Use the lowest dose that still gives a useful result.
16.Ultrasound imaging works by:
Answer: B
Echo times give the depths of the boundaries.
17.Ultrasound is used to scan unborn babies because:
Answer: C
It does not damage the developing baby's cells.
18.A gel is applied to the skin before an ultrasound scan to:
Answer: D
Air at the skin would reflect almost all the ultrasound.
19.MRI (magnetic resonance imaging) uses:
Answer: A
Hydrogen nuclei in the body respond to the field and radio pulses.
20.An advantage of MRI over CT scanning is that MRI:
Answer: D
It is good for brain and joint imaging.
21.Patients with metal implants or pacemakers may not be allowed an MRI scan because:
Answer: B
This is a safety risk.
22.In a gamma camera scan, the patient is given:
Answer: B
The camera detects where the tracer collects.
23.A tracer used inside the body should have:
Answer: B
Gamma rays can be detected outside the body; a short half-life limits the dose.
24.Radiotherapy treats cancer by:
Answer: D
High-energy beams are aimed at the tumour.
25.In radiotherapy, the beam is aimed at the tumour from several directions so that:
Answer: C
The beams overlap only at the tumour.
26.Which imaging method gives a 3D picture by combining many X-ray images?
Answer: D
A computer builds cross-sectional slices.
27.An endoscope uses:
Answer: D
Light travels along fibres by total internal reflection.
28.Radiation damages living cells mainly by:
Answer: A
Damage can kill cells or cause mutations.
29.Large doses of radiation received in a short time can cause:
Answer: A
These are deterministic effects that appear above a threshold dose.
30.The dose rate of a source is 2 mGy per hour. What dose is received in 3 hours?
Answer: B
Dose = rate × time = 2 × 3 = 6 mGy.
31.The gray is the unit of absorbed dose.
Answer: True
1 Gy = 1 J/kg.
32.Ultrasound is a form of ionising radiation.
Answer: False
Ultrasound is a sound wave and is non-ionising.
33.Increasing the distance from a radiation source reduces the dose received.
Answer: True
Intensity falls with distance.
34.MRI scans use X-rays to form images.
Answer: False
MRI uses magnetic fields and radio waves.
35.Background radiation is present everywhere at a low level.
Answer: True
It comes from natural and artificial sources.
36.The unit of equivalent dose is the ______.
Answer: sievert (Sv)
Named after Rolf Sievert.
37.Radiation with enough energy to remove electrons from atoms is called ______ radiation.
Answer: ionising (ionizing)
X-rays and gamma rays are examples.
38.Imaging that uses strong magnetic fields and radio waves is called ______.
Answer: MRI (magnetic resonance imaging)
It uses no ionising radiation.
39.The use of radiation to destroy cancer cells is called ______.
Answer: radiotherapy (radiation therapy)
Beams are aimed at the tumour.
40.Time, distance and ______ are the three ways to reduce radiation exposure.
Answer: shielding
Lead and concrete are common shields.
1.Semiconductors have electrical conductivity that is:
Answer: B
Semiconductors have conductivity intermediate between good conductors (metals) and insulators, and this conductivity increases with temperature.
2.Doping a semiconductor means:
Answer: B
Doping introduces controlled amounts of impurity atoms into a pure (intrinsic) semiconductor to modify its electrical conductivity.
3.An n-type semiconductor is formed by doping with atoms that:
Answer: A
Doping with pentavalent atoms (like phosphorus in silicon) adds extra free electrons, creating an n-type (negative charge carrier) semiconductor.
4.A p-type semiconductor is formed by doping with atoms that:
Answer: C
Doping with trivalent atoms (like boron in silicon) creates electron deficiencies called 'holes', which act as positive charge carriers.
5.A p-n junction diode allows current to flow easily when:
Answer: A
In forward bias, the p-n junction's depletion region narrows, allowing current to flow easily through the diode.
6.In reverse bias, a p-n junction diode:
Answer: D
Reverse bias widens the depletion region, blocking the flow of majority carriers and allowing only a very small leakage current.
7.A half-wave rectifier uses:
Answer: A
A half-wave rectifier uses a single diode, which conducts during only one half-cycle of the AC input, blocking the other half.
8.A full-wave rectifier, compared to a half-wave rectifier, produces:
Answer: B
A full-wave rectifier uses both halves of the AC cycle (using two or four diodes), producing a smoother and more continuous DC output.
9.A transistor is a semiconductor device with:
Answer: A
A bipolar junction transistor has three regions (emitter, base, collector) forming two p-n junctions.
10.An NPN transistor consists of:
Answer: C
An NPN transistor has a thin p-type base sandwiched between two n-type regions (emitter and collector).
11.A transistor can be used as an electronic switch because:
Answer: B
By controlling a small base current, a transistor can switch a much larger current in the collector circuit on or off, acting as an electronic switch.
12.A transistor used as an amplifier works because:
Answer: D
In amplifier configuration, small variations in base current cause proportionally much larger variations in collector current, providing signal amplification.
13.The output of an AND logic gate is HIGH only when:
Answer: B
An AND gate outputs HIGH (1) only when every one of its inputs is HIGH (1); otherwise the output is LOW (0).
14.The output of an OR logic gate is HIGH when:
Answer: C
An OR gate outputs HIGH if any one (or more) of its inputs is HIGH.
15.A NOT gate (inverter) has:
Answer: C
A NOT gate has a single input and produces an output that is the logical inverse (opposite) of that input.
16.Silicon and germanium are commonly used semiconductors because they:
Answer: D
Silicon and germanium each have four valence electrons, forming a stable crystal lattice that can be precisely doped to create n-type or p-type materials.
17.The region at a p-n junction with no free charge carriers is called the:
Answer: A
The depletion region is a narrow zone at the p-n junction depleted of free charge carriers, formed by recombination near the junction.
18.Increasing temperature generally ___ the conductivity of a pure (intrinsic) semiconductor.
Answer: B
As temperature rises, more electron-hole pairs are thermally generated in a semiconductor, increasing its conductivity (opposite to the trend in metals).
19.A light-emitting diode (LED) emits light when:
Answer: B
An LED emits light in forward bias, as electrons and holes recombine at the junction and release energy in the form of photons.
20.A photodiode is a semiconductor device that:
Answer: D
A photodiode's current changes in response to incident light, making it useful as a light sensor.
21.A solar cell converts:
Answer: B
A solar (photovoltaic) cell is a semiconductor device that converts light energy directly into electrical energy.
22.The base region of a transistor is typically:
Answer: A
The base region is deliberately made thin and lightly doped so that most carriers injected from the emitter pass through to the collector, enabling amplification.
23.Combining an AND gate and a NOT gate in series produces which gate?
Answer: C
An AND gate followed by a NOT (inverter) gate produces a NAND gate, whose output is the complement of the AND output.
24.A capacitor used as a filter after a rectifier serves to:
Answer: A
A smoothing capacitor charges during peaks and discharges between them, reducing the ripple in a rectified DC output.
25.Zener diodes are specially designed to operate in:
Answer: D
Zener diodes are designed to safely operate in reverse breakdown at a specific voltage, making them useful for voltage regulation.
26.The main advantage of transistors over older vacuum tubes includes:
Answer: C
Transistors are much smaller, consume less power, generate less heat, and are more reliable and durable than vacuum tubes.
27.In a common-emitter transistor amplifier, the output signal is typically:
Answer: D
A common-emitter amplifier configuration produces an output signal that is inverted (180° phase shift) relative to the input signal.
28.A logic circuit that outputs HIGH only when its two inputs differ is called:
Answer: C
An XOR gate outputs HIGH only when its two inputs are different (one HIGH, one LOW); if both are the same, the output is LOW.
29.Which is a common application of transistors in digital electronics?
Answer: D
Transistors act as fast electronic switches, forming the basic building blocks of digital logic circuits representing binary states.
30.A rectifier followed by a smoothing capacitor and voltage regulator forms a basic:
Answer: A
This combination (rectifier + smoothing + regulation) forms a typical DC power supply, converting AC mains into stable DC output.
31.A p-type semiconductor has majority charge carriers that are electrons.
Answer: False
In a p-type semiconductor, the majority charge carriers are holes (positive), not electrons.
32.A diode conducts easily in forward bias and blocks current in reverse bias.
Answer: True
This is the defining behaviour of a p-n junction diode: low resistance when forward biased, high resistance when reverse biased.
33.A transistor can amplify a signal because a small base current controls a much larger collector current.
Answer: True
This current-controlling behaviour is exactly how a transistor achieves amplification of small signals.
34.An OR gate outputs HIGH only when all of its inputs are HIGH.
Answer: False
That description applies to an AND gate; an OR gate outputs HIGH if at least one input is HIGH.
35.Increasing temperature always decreases the conductivity of a semiconductor.
Answer: False
Unlike metals, increasing temperature generally increases the conductivity of a semiconductor, as more charge carriers are thermally generated.
36.A semiconductor doped to have excess free electrons is called ______-type.
Answer: n
n-type semiconductors are doped with pentavalent impurities, providing extra free electrons as majority carriers.
37.A semiconductor doped to have a deficiency of electrons (excess holes) is called ______-type.
Answer: p
p-type semiconductors are doped with trivalent impurities, creating holes as majority carriers.
38.The process of converting AC into DC using diodes is called ______.
Answer: rectification
Rectification is the process of converting alternating current into direct current, typically using diodes.
39.A transistor has three regions called the emitter, base, and ______.
Answer: collector
The three regions of a bipolar junction transistor are the emitter, base, and collector.
40.A logic gate that inverts its single input is called a ______ gate.
Answer: NOT
The NOT gate (inverter) produces an output that is the logical opposite of its single input.
1.Cosmology is the study of:
Answer: C
It deals with the universe on the largest scales.
2.A galaxy is:
Answer: A
The Milky Way is our galaxy.
3.Our galaxy is called the:
Answer: C
It is a spiral galaxy.
4.The Milky Way is a:
Answer: A
It has spiral arms around a central bulge.
5.The diameter of the Milky Way is about:
Answer: D
About 100 000 light-years across.
6.The three main types of galaxies by shape are:
Answer: C
This is the Hubble classification.
7.A light-year is a unit of:
Answer: D
The distance light travels in one year, about 9.46 × 10¹⁵ m.
8.A light-year is about:
Answer: B
3 × 10⁸ m/s × 3.15 × 10⁷ s ≈ 9.46 × 10¹⁵ m.
9.The distance from the Earth to the Sun (about 1.5 × 10¹¹ m) is called:
Answer: D
1 AU is the mean Earth–Sun distance.
10.Groups of galaxies held together by gravity are called:
Answer: B
Our Local Group contains the Milky Way and Andromeda.
11.Light from distant galaxies is shifted towards longer wavelengths. This is called:
Answer: A
Redshift shows the galaxy is moving away from us.
12.Redshift of distant galaxies is evidence that:
Answer: C
Almost all distant galaxies are receding.
13.Hubble's law states that:
Answer: C
v = H₀d.
14.In Hubble's law v = H₀d, H₀ is called the:
Answer: C
It is about 70 km/s per megaparsec.
15.Using H₀ = 70 km/s/Mpc, how fast does a galaxy 100 Mpc away recede?
Answer: A
v = H₀d = 70 × 100 = 7000 km/s.
16.The age of the universe can be estimated from:
Answer: B
If the universe has expanded at a steady rate, its age ≈ 1/H₀ (about 14 billion years).
17.The Big Bang theory states that the universe:
Answer: B
This is the main scientific model of the universe's origin.
18.The cosmic microwave background (CMB) radiation is evidence for:
Answer: B
It is the cooled leftover radiation from the early hot universe.
19.The temperature of the cosmic microwave background is about:
Answer: A
It is very cold today because the universe has expanded.
20.Stars form from:
Answer: A
Gravity pulls the material together until fusion begins.
21.A star produces energy mainly by:
Answer: D
Fusion in the core releases enormous energy.
22.Our Sun is a:
Answer: B
It is fusing hydrogen steadily in its core.
23.When a star like the Sun runs out of hydrogen in its core, it will become a:
Answer: A
Low-mass stars swell, shed their outer layers and leave a white dwarf.
24.A very massive star ends its life in a:
Answer: D
Massive stars collapse violently.
25.A black hole is a region where:
Answer: C
It forms when a massive core collapses.
26.The parsec is a unit of distance equal to about:
Answer: B
1 pc ≈ 3.26 ly ≈ 3.09 × 10¹⁶ m.
27.The distance to nearby stars can be measured using:
Answer: D
The star's apparent shift as Earth orbits the Sun gives its distance.
28.A star has a parallax angle of 0.5 arcseconds. What is its distance? (d = 1/p)
Answer: B
d = 1 ÷ 0.5 = 2 parsecs.
29.Light from a galaxy 1 billion light-years away shows us the galaxy as it was:
Answer: D
The light took 1 billion years to reach us.
30.Elliptical galaxies mainly contain:
Answer: A
Star formation has mostly stopped in elliptical galaxies.
31.A light-year is a unit of time.
Answer: False
It is a unit of distance.
32.The redshift of distant galaxies shows that the universe is expanding.
Answer: True
Galaxies are moving away from us.
33.Stars produce energy by nuclear fission.
Answer: False
Stars produce energy by nuclear fusion.
34.The cosmic microwave background is evidence for the Big Bang.
Answer: True
It is leftover radiation from the early universe.
35.In Hubble's law, more distant galaxies recede faster.
Answer: True
v = H₀d.
36.The theory that the universe began from a hot, dense state and has been expanding is the Big ______ theory.
Answer: Bang
About 13.8 billion years ago.
37.Our galaxy is called the ______ Way.
Answer: Milky
A spiral galaxy.
38.The shift of light from receding galaxies towards longer wavelengths is called ______.
Answer: redshift
It shows they are moving away.
39.Hubble's law is written v = H₀ × ______.
Answer: d (distance)
Recession speed is proportional to distance.
40.The final stage of a very massive star, from which light cannot escape, is a black ______.
Answer: hole
Formed after a supernova.