QA A LEVEL PHYSICS 2021 PAPER 3 QP ALL
COMPONENTS EXAM with Questions and
Answers/Plus a Rationale Updated 2026 A+/Instant
Download PDF
EXAM COVERAGE
1. Practical Skills and Experimental Techniques
2. Data Analysis and Uncertainty Evaluation
3. Mechanics and Materials
4. Thermal Physics and Gases
5. Fields and Their Consequences
6. Nuclear and Particle Physics
7. Electronics and Circuit Analysis
8. Astrophysics and Cosmology
1. A student performs an experiment to determine the Young modulus of a metal wire. When
plotting the stress-strain graph, the student observes that the data points do not form a perfectly
straight line at the origin due to the wire not being fully taut. Which action best addresses this
systematic error during analysis?
A. Omitting the first three data points and calculating the gradient from the remaining linear
section.
B. Adding an intercept correction to the stress values based on the extrapolation of the
linear region back to the strain axis.
, C. Increasing the number of repeated measurements at the lowest load to reduce the random
uncertainty.
D. Ignoring the non-linearity as it represents a negligible percentage of the total wire extension.
Answer: B
CORRECT ANSWER : B
Rationale: An intercept correction accounts for the initial slack in the wire system, ensuring the
true gradient (Young modulus) is accurately derived from the linear region. Option A is
statistically unsound as it discards valid data without correcting the systematic bias, C addresses
random error rather than systematic, and D ignores a fundamental flaw in the experimental
setup.
2. In an investigation of the internal resistance of a cell, a student records terminal potential
difference (V) against current (I). The graph of V against I yields a gradient of -1.5 $\Omega$. If
the experiment is repeated using an ammeter with a non-negligible resistance, how will the
calculated internal resistance compare to the true value?
A. It will be lower because the ammeter resistance is added to the external circuit.
B. It will be higher because the ammeter resistance is treated as part of the total circuit
resistance.
C. It will remain unchanged because the gradient is independent of external resistance.
D. It will be lower due to the increased current flowing through the circuit.
Answer: B
CORRECT ANSWER : B
Rationale: In the equation $V = E - I(r + R_{ext})$, where $R_{ext}$ includes the ammeter
resistance, the measured gradient reflects $-(r + R_{ammeter})$. Therefore, the calculated
internal resistance ($r$) will be overestimated by the value of the ammeter resistance. Options A,
C, and D misinterpret the effect of adding resistance to the series circuit.
3. During an experiment involving the specific heat capacity of a solid, a student fails to account
for thermal energy loss to the surroundings during the cooling phase. Which effect does this have
on the calculated value of specific heat capacity?
A. It will be overestimated because the temperature change ($\Delta\theta$) appears larger than it
actually is.
, B. It will be overestimated because the energy required to reach the observed temperature
change appears higher than it is.
C. It will be underestimated because the temperature change ($\Delta\theta$) is smaller than
expected.
D. It will remain unchanged as the energy balance equation is independent of heat loss.
Answer: B
CORRECT ANSWER : B
Rationale: If heat is lost to the surroundings, the measured temperature rise is lower than it
would be in an adiabatic system. Since $c = \frac{Q}{m\Delta\theta}$, and the measured
$\Delta\theta$ is artificially low for a given input energy $Q$, the calculated $c$ becomes
artificially high. Options A, C, and D are incorrect based on the algebraic relationship in the
specific heat formula.
4. A circuit is designed to measure the variation of resistance with temperature for a thermistor. The
student notices that as the current increases, the resistance drops significantly faster than
expected. What is the most likely cause?
A. The thermistor has reached its Curie temperature.
B. Joule heating of the thermistor is increasing its temperature independently of the bath.
C. The ammeter is experiencing a calibration drift due to current saturation.
D. The battery voltage is fluctuating, leading to inconsistent readings.
Answer: B
CORRECT ANSWER : B
Rationale: Thermistors are sensitive to their own internal heating ($I^2R$ losses); if the current
is too high, the thermistor self-heats, changing its resistance and invalidating the temperature-
resistance relationship. Option A is irrelevant to thermistor physics, and C and D suggest
equipment failure which is less likely than the physical limitation of the component.
5. A student investigates the diffraction of monochromatic light through a double slit. If the slit
separation $s$ is measured with a micrometer and the fringe width $w$ is measured using a
traveling microscope, which choice represents the most effective way to minimize the percentage
uncertainty in the wavelength $\lambda$?
A. Using a laser with a shorter wavelength to increase the fringe separation.
, B. Measuring the distance across ten fringe widths to reduce the percentage uncertainty in
$w$.
C. Reducing the distance between the slits and the screen to increase fringe intensity.
D. Increasing the width of the individual slits to sharpen the interference pattern.
Answer: B
CORRECT ANSWER : B
Rationale: The uncertainty in a single measurement of $w$ is high due to the difficulty of
pinpointing fringe centers. Measuring $N$ fringes reduces the absolute uncertainty in the total
distance and thus decreases the percentage uncertainty in $w$. Options A, C, and D either do
not address uncertainty or negatively impact the resolution of the experiment.
6. In a pendulum experiment, a student measures the period $T$ for 20 oscillations. If the
uncertainty in the time measurement is $\pm 0.1$ s, what is the uncertainty in the period $T$?
A. $\pm 0.1$ s
B. $\pm 0.05$ s
C. $\pm 0.005$ s
D. $\pm 2.0$ s
Answer: C
CORRECT ANSWER : C
Rationale: The uncertainty in the period $T$ is the uncertainty of the total time divided by the
number of oscillations $N$. Thus, $\frac{0.1}{20} = 0.005$ s. Options A, B, and D represent
incorrect mathematical treatments of propagation of uncertainty.
7. When calibrating a voltmeter against a standard cell, the student finds a consistent offset of
$+0.2$ V across all readings. How should this be handled to maintain the validity of the data?
A. Discard all readings and replace the voltmeter.
B. Apply a zero-error correction of $-0.2$ V to all recorded values.
C. Include the $+0.2$ V in the uncertainty calculation as a random error.
D. Ignore the error, as it will cancel out when calculating the gradient of a graph.
COMPONENTS EXAM with Questions and
Answers/Plus a Rationale Updated 2026 A+/Instant
Download PDF
EXAM COVERAGE
1. Practical Skills and Experimental Techniques
2. Data Analysis and Uncertainty Evaluation
3. Mechanics and Materials
4. Thermal Physics and Gases
5. Fields and Their Consequences
6. Nuclear and Particle Physics
7. Electronics and Circuit Analysis
8. Astrophysics and Cosmology
1. A student performs an experiment to determine the Young modulus of a metal wire. When
plotting the stress-strain graph, the student observes that the data points do not form a perfectly
straight line at the origin due to the wire not being fully taut. Which action best addresses this
systematic error during analysis?
A. Omitting the first three data points and calculating the gradient from the remaining linear
section.
B. Adding an intercept correction to the stress values based on the extrapolation of the
linear region back to the strain axis.
, C. Increasing the number of repeated measurements at the lowest load to reduce the random
uncertainty.
D. Ignoring the non-linearity as it represents a negligible percentage of the total wire extension.
Answer: B
CORRECT ANSWER : B
Rationale: An intercept correction accounts for the initial slack in the wire system, ensuring the
true gradient (Young modulus) is accurately derived from the linear region. Option A is
statistically unsound as it discards valid data without correcting the systematic bias, C addresses
random error rather than systematic, and D ignores a fundamental flaw in the experimental
setup.
2. In an investigation of the internal resistance of a cell, a student records terminal potential
difference (V) against current (I). The graph of V against I yields a gradient of -1.5 $\Omega$. If
the experiment is repeated using an ammeter with a non-negligible resistance, how will the
calculated internal resistance compare to the true value?
A. It will be lower because the ammeter resistance is added to the external circuit.
B. It will be higher because the ammeter resistance is treated as part of the total circuit
resistance.
C. It will remain unchanged because the gradient is independent of external resistance.
D. It will be lower due to the increased current flowing through the circuit.
Answer: B
CORRECT ANSWER : B
Rationale: In the equation $V = E - I(r + R_{ext})$, where $R_{ext}$ includes the ammeter
resistance, the measured gradient reflects $-(r + R_{ammeter})$. Therefore, the calculated
internal resistance ($r$) will be overestimated by the value of the ammeter resistance. Options A,
C, and D misinterpret the effect of adding resistance to the series circuit.
3. During an experiment involving the specific heat capacity of a solid, a student fails to account
for thermal energy loss to the surroundings during the cooling phase. Which effect does this have
on the calculated value of specific heat capacity?
A. It will be overestimated because the temperature change ($\Delta\theta$) appears larger than it
actually is.
, B. It will be overestimated because the energy required to reach the observed temperature
change appears higher than it is.
C. It will be underestimated because the temperature change ($\Delta\theta$) is smaller than
expected.
D. It will remain unchanged as the energy balance equation is independent of heat loss.
Answer: B
CORRECT ANSWER : B
Rationale: If heat is lost to the surroundings, the measured temperature rise is lower than it
would be in an adiabatic system. Since $c = \frac{Q}{m\Delta\theta}$, and the measured
$\Delta\theta$ is artificially low for a given input energy $Q$, the calculated $c$ becomes
artificially high. Options A, C, and D are incorrect based on the algebraic relationship in the
specific heat formula.
4. A circuit is designed to measure the variation of resistance with temperature for a thermistor. The
student notices that as the current increases, the resistance drops significantly faster than
expected. What is the most likely cause?
A. The thermistor has reached its Curie temperature.
B. Joule heating of the thermistor is increasing its temperature independently of the bath.
C. The ammeter is experiencing a calibration drift due to current saturation.
D. The battery voltage is fluctuating, leading to inconsistent readings.
Answer: B
CORRECT ANSWER : B
Rationale: Thermistors are sensitive to their own internal heating ($I^2R$ losses); if the current
is too high, the thermistor self-heats, changing its resistance and invalidating the temperature-
resistance relationship. Option A is irrelevant to thermistor physics, and C and D suggest
equipment failure which is less likely than the physical limitation of the component.
5. A student investigates the diffraction of monochromatic light through a double slit. If the slit
separation $s$ is measured with a micrometer and the fringe width $w$ is measured using a
traveling microscope, which choice represents the most effective way to minimize the percentage
uncertainty in the wavelength $\lambda$?
A. Using a laser with a shorter wavelength to increase the fringe separation.
, B. Measuring the distance across ten fringe widths to reduce the percentage uncertainty in
$w$.
C. Reducing the distance between the slits and the screen to increase fringe intensity.
D. Increasing the width of the individual slits to sharpen the interference pattern.
Answer: B
CORRECT ANSWER : B
Rationale: The uncertainty in a single measurement of $w$ is high due to the difficulty of
pinpointing fringe centers. Measuring $N$ fringes reduces the absolute uncertainty in the total
distance and thus decreases the percentage uncertainty in $w$. Options A, C, and D either do
not address uncertainty or negatively impact the resolution of the experiment.
6. In a pendulum experiment, a student measures the period $T$ for 20 oscillations. If the
uncertainty in the time measurement is $\pm 0.1$ s, what is the uncertainty in the period $T$?
A. $\pm 0.1$ s
B. $\pm 0.05$ s
C. $\pm 0.005$ s
D. $\pm 2.0$ s
Answer: C
CORRECT ANSWER : C
Rationale: The uncertainty in the period $T$ is the uncertainty of the total time divided by the
number of oscillations $N$. Thus, $\frac{0.1}{20} = 0.005$ s. Options A, B, and D represent
incorrect mathematical treatments of propagation of uncertainty.
7. When calibrating a voltmeter against a standard cell, the student finds a consistent offset of
$+0.2$ V across all readings. How should this be handled to maintain the validity of the data?
A. Discard all readings and replace the voltmeter.
B. Apply a zero-error correction of $-0.2$ V to all recorded values.
C. Include the $+0.2$ V in the uncertainty calculation as a random error.
D. Ignore the error, as it will cancel out when calculating the gradient of a graph.
