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A Level H1 Physics Electricity Magnetism Quiz

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Questions

A-Level Physics H1 Quiz - Electricity Magnetism

Name: __________________________
Class: __________________________
Date: __________________________
Score: _______ / 45

Duration: 60 minutes
Total Marks: 45

Instructions:

Answer all questions.
Show all working clearly. Marks are awarded for correct method and logical steps.
Use $g = 9.81 \text{ m s}^{-2}$ where necessary (though not required for this topic).
Standard constants: $e = 1.60 \times 10^{-19} \text{ C}$ , $c = 3.00 \times 10^8 \text{ m s}^{-1}$ .

Section A: Multiple Choice & Short Concepts (Questions 1–5)

[5 marks]

1. Which of the following correctly defines the electromotive force (e.m.f.) of a battery? A. The energy supplied by the battery to drive unit charge around the complete circuit. B. The potential difference across the terminals of the battery when no current flows. C. The force exerted by the battery on the electrons. D. The power delivered by the battery per unit current.

2. Two wires X and Y are made of the same material. Wire X has length $L$ and cross-sectional area $A$ . Wire Y has length $2L$ and cross-sectional area $A/2$ . What is the ratio of the resistance of wire Y to the resistance of wire X? A. 1 : 1 B. 2 : 1 C. 4 : 1 D. 8 : 1

3. A battery with e.m.f. $\mathcal{E}$ and internal resistance $r$ is connected to a variable resistor $R$ . As the resistance $R$ is increased, which of the following quantities decreases? A. The terminal potential difference. B. The current in the circuit. C. The power dissipated in the internal resistance. D. Both B and C.

4. In a potential divider circuit consisting of a fixed resistor $R_1$ and a thermistor $R_2$ connected in series across a supply, the output voltage is taken across the thermistor. What happens to the output voltage as the temperature of the thermistor increases? A. It increases. B. It decreases. C. It remains constant. D. It becomes zero.

5. State the condition required for the principle of conservation of charge to hold in a circuit junction.

[1]

Section B: Circuit Analysis & Calculations (Questions 6–10)

[15 marks]

6. A copper wire has a length of $1.5 \text{ m}$ and a cross-sectional area of $0.50 \text{ mm}^2$ . The resistivity of copper is $1.7 \times 10^{-8} \Omega \text{ m}$ . (a) Calculate the resistance of the wire. [2]

(b) If a current of $2.0 \text{ A}$ flows through the wire, calculate the potential difference across its ends. [1]

7. A battery has an e.m.f. of $12.0 \text{ V}$ and an internal resistance of $0.50 \Omega$ . It is connected to a lamp of resistance $5.5 \Omega$ . (a) Calculate the current flowing in the circuit. [2]

(b) Calculate the terminal potential difference across the battery. [2]

8. The graph below shows the variation of current $I$ with potential difference $V$ for a filament lamp.

(Imagine a curve starting at origin, gradient decreasing as V increases)

(a) Explain, in terms of the motion of electrons and lattice ions, why the resistance of the filament increases as the potential difference increases. [3]

(b) Determine the resistance of the lamp when the potential difference is $6.0 \text{ V}$ , given that the current at this voltage is $0.40 \text{ A}$ . [1]

9. Consider the circuit shown below:

A $12 \text{ V}$ battery with negligible internal resistance.
A fixed resistor $R_1 = 4.0 \Omega$ in series with a parallel combination.
The parallel combination consists of resistor $R_2 = 6.0 \Omega$ and resistor $R_3 = 3.0 \Omega$ .

(a) Calculate the total resistance of the parallel combination. [2]

(b) Calculate the total current supplied by the battery. [2]

10. A student sets up a potential divider using a $100 \Omega$ potentiometer connected across a $6.0 \text{ V}$ supply. A voltmeter is connected between the slider and the negative terminal. (a) Explain why the voltmeter reading changes as the slider is moved. [2]

(b) If the slider is positioned such that the resistance between the slider and the negative terminal is $40 \Omega$ , calculate the voltmeter reading (assume the voltmeter has infinite resistance). [2]

Section C: Structured Problems & Applications (Questions 11–15)

[15 marks]

11. Kirchhoff’s Laws are essential for analyzing complex circuits. (a) State Kirchhoff’s First Law. [1]

(b) State Kirchhoff’s Second Law. [1]

(c) In a circuit loop, a battery of e.m.f. $9.0 \text{ V}$ is connected in series with two resistors, $R_A$ and $R_B$ . The potential difference across $R_A$ is measured to be $3.0 \text{ V}$ . Using Kirchhoff’s Second Law, determine the potential difference across $R_B$ . [2]

12. A heating element is rated at $240 \text{ V}$ , $1.2 \text{ kW}$ . (a) Calculate the current flowing through the element when operating at normal brightness. [2]

(b) Calculate the resistance of the heating element at operating temperature. [2]

(c) If the element is connected to a $120 \text{ V}$ supply, calculate the new power output, assuming the resistance remains constant. [2]

13. Two identical cells, each with e.m.f. $1.5 \text{ V}$ and internal resistance $0.2 \Omega$ , are connected in series to an external load resistor of $5.6 \Omega$ . (a) Calculate the total e.m.f. of the combination. [1]

(b) Calculate the total internal resistance of the combination. [1]

14. A light-dependent resistor (LDR) is used in a street-light switching circuit. The LDR is connected in series with a fixed resistor $R$ across a $12 \text{ V}$ supply. The output voltage is taken across the LDR. (a) Describe how the resistance of the LDR changes as light intensity increases. [1]

(b) Explain whether the output voltage across the LDR increases or decreases as it gets darker. [2]

15. A wire of length $L$ and resistance $R$ is stretched uniformly to twice its original length ( $2L$ ). Assume the volume of the wire remains constant. (a) State the new cross-sectional area in terms of the original area $A$ . [1]

(b) Show that the new resistance of the wire is $4R$ . [2]

Section D: Advanced Concepts & Synthesis (Questions 16–20)

[10 marks]

16. A student investigates the I-V characteristic of a semiconductor diode. (a) Sketch the I-V graph for a silicon diode, labeling the axes and indicating the approximate threshold voltage. [2]

(b) Explain why the diode conducts current in only one direction. [1]

17. Define the term "drift velocity" of electrons in a conductor.

[1]

18. A high-voltage transmission line carries a current of $500 \text{ A}$ at a voltage of $400 \text{ kV}$ . (a) Calculate the power transmitted. [1]

(b) Explain why high voltages are used for long-distance power transmission. [1]

19. In a circuit, three resistors of $2 \Omega$ , $3 \Omega$ , and $6 \Omega$ are connected in parallel. (a) Calculate the equivalent resistance of this combination. [2]

20. A capacitor is charged by a battery and then disconnected. It is then connected across a resistor. (a) Describe what happens to the charge stored on the capacitor plates over time. [1]

(b) State the form of energy conversion that occurs in the resistor during this process. [1]

Answers

A-Level Physics H1 Quiz - Electricity Magnetism (Answer Key)

1. A

Reasoning: E.m.f. is defined as the energy converted from non-electrical to electrical form per unit charge passing through the source. B is the definition of terminal p.d. when $I=0$ (which equals e.m.f. numerically but is not the definition of the source's energy conversion capability).

2. C

Reasoning: $R = \rho \frac{L}{A}$ . $R_X = \rho \frac{L}{A}$ . $R_Y = \rho \frac{2L}{A/2} = \rho \frac{4L}{A} = 4 R_X$ . Ratio $R_Y : R_X = 4 : 1$ .

3. D

Reasoning: As $R$ increases, total resistance $(R+r)$ increases. Current $I = \frac{\mathcal{E}}{R+r}$ decreases (B is correct). Power in internal resistance $P_r = I^2 r$ . Since $I$ decreases, $P_r$ decreases (C is correct). Terminal p.d. $V = \mathcal{E} - Ir$ . As $I$ decreases, $Ir$ decreases, so $V$ increases. Thus A is incorrect.

4. B

Reasoning: For an NTC thermistor, resistance decreases as temperature increases. In a potential divider, $V_{out} = V_{in} \frac{R_{thermistor}}{R_{total}}$ . If $R_{thermistor}$ decreases, its share of the voltage decreases.

5. The sum of currents entering a junction equals the sum of currents leaving the junction.

Marking: [B1] for "sum of currents in = sum of currents out" or $\sum I_{in} = \sum I_{out}$ .

6. (a) Calculation: $R = \rho \frac{L}{A}$ $A = 0.50 \text{ mm}^2 = 0.50 \times 10^{-6} \text{ m}^2$ $R = \frac{1.7 \times 10^{-8} \times 1.5}{0.50 \times 10^{-6}}$ $R = \frac{2.55 \times 10^{-8}}{0.50 \times 10^{-6}} = 5.1 \times 10^{-2} \Omega$ or $0.051 \Omega$ [M1] for formula/substitution, [A1] for answer.

(b) Calculation: $V = IR = 2.0 \times 0.051 = 0.102 \text{ V}$ [B1] for answer.

7. (a) Calculation: $I = \frac{\mathcal{E}}{R + r} = \frac{12.0}{5.5 + 0.50} = \frac{12.0}{6.0} = 2.0 \text{ A}$ [M1] for correct circuit equation, [A1] for answer.

(b) Calculation: $V = \mathcal{E} - Ir = 12.0 - (2.0 \times 0.50) = 12.0 - 1.0 = 11.0 \text{ V}$ Alternatively $V = IR = 2.0 \times 5.5 = 11.0 \text{ V}$ [M1] for method, [A1] for answer.

8. (a) Explanation: 1. As p.d. increases, current increases, causing the temperature of the filament to rise. [B1] 2. The lattice ions vibrate with greater amplitude. [B1] 3. This increases the frequency of collisions between free electrons and lattice ions, impeding electron flow (increasing resistance). [B1]

(b) Calculation: $R = \frac{V}{I} = \frac{6.0}{0.40} = 15 \Omega$ [B1] for answer.

9. (a) Calculation: $\frac{1}{R_p} = \frac{1}{R_2} + \frac{1}{R_3} = \frac{1}{6.0} + \frac{1}{3.0} = \frac{1}{6} + \frac{2}{6} = \frac{3}{6}$ $R_p = \frac{6}{3} = 2.0 \Omega$ [M1] for parallel formula, [A1] for answer.

(b) Calculation: $R_{total} = R_1 + R_p = 4.0 + 2.0 = 6.0 \Omega$ $I_{total} = \frac{V}{R_{total}} = \frac{12}{6.0} = 2.0 \text{ A}$ [M1] for total R, [A1] for current.

(c) Calculation: $V_{R2} = V_{parallel} = I_{total} \times R_p = 2.0 \times 2.0 = 4.0 \text{ V}$ [M1] for method, [A1] for answer.

10. (a) Explanation: Moving the slider changes the ratio of the resistances in the two parts of the potentiometer. Since the potential difference is distributed proportionally to resistance in a series circuit, changing the resistance across the voltmeter changes the voltage drop across it. [B1] for mentioning resistance ratio/change, [B1] for linking to p.d. distribution.

(b) Calculation: $V_{out} = V_{in} \times \frac{R_{part}}{R_{total}}$ $V_{out} = 6.0 \times \frac{40}{100} = 6.0 \times 0.4 = 2.4 \text{ V}$ [M1] for potential divider formula, [A1] for answer.

11. (a) Statement: The sum of currents entering a junction is equal to the sum of currents leaving the junction. (Conservation of Charge). [B1]

(b) Statement: The sum of e.m.f.s in any closed loop is equal to the sum of potential differences (voltage drops) in that loop. (Conservation of Energy). [B1]

(c) Calculation: $\mathcal{E} = V_A + V_B$ $9.0 = 3.0 + V_B$ $V_B = 6.0 \text{ V}$ [M1] for applying KVL, [A1] for answer.

12. (a) Calculation: $P = VI \Rightarrow I = \frac{P}{V} = \frac{1200}{240} = 5.0 \text{ A}$ [M1] for rearrangement, [A1] for answer.

(b) Calculation: $R = \frac{V}{I} = \frac{240}{5.0} = 48 \Omega$ Or $R = \frac{V^2}{P} = \frac{240^2}{1200} = 48 \Omega$ [M1] for method, [A1] for answer.

(c) Calculation: $P_{new} = \frac{V_{new}^2}{R} = \frac{120^2}{48} = \frac{14400}{48} = 300 \text{ W}$ [M1] for method, [A1] for answer.

13. (a) Calculation: Cells in series: $\mathcal{E}_{total} = 1.5 + 1.5 = 3.0 \text{ V}$ [B1]

(b) Calculation: Internal resistances in series: $r_{total} = 0.2 + 0.2 = 0.4 \Omega$ [B1]

(c) Calculation: $I = \frac{\mathcal{E}_{total}}{R + r_{total}} = \frac{3.0}{5.6 + 0.4} = \frac{3.0}{6.0} = 0.50 \text{ A}$ [M1] for correct total values, [A1] for answer.

14. (a) Description: The resistance of the LDR decreases as light intensity increases. [B1]

(b) Explanation: 1. As it gets darker, the resistance of the LDR increases. [B1] 2. In a series potential divider, a larger resistance takes a larger share of the supply voltage. Therefore, the output voltage across the LDR increases. [B1]

15. (a) Statement: Volume $V = L \times A = \text{constant}$ . New Length $L' = 2L$ . $L A = (2L) A' \Rightarrow A' = \frac{A}{2}$ [B1]

(b) Proof: $R = \rho \frac{L}{A}$ $R' = \rho \frac{L'}{A'} = \rho \frac{2L}{A/2} = \rho \frac{4L}{A} = 4 \left( \rho \frac{L}{A} \right) = 4R$ [M1] for substitution of new dimensions, [A1] for showing final result.

16. (a) Sketch: Graph should show negligible current for $V < 0.6 \text{ V}$ (approx), then sharp exponential increase for $V > 0.6 \text{ V}$ . Reverse bias shows negligible current. [B1] for shape, [B1] for labels/threshold.

(b) Explanation: The p-n junction allows current to flow easily when forward-biased (p-side to positive) but creates a high resistance barrier when reverse-biased. [B1]

17. Definition: The average velocity attained by charged particles, such as electrons, in a material due to an electric field. [B1]

18. (a) Calculation: $P = VI = 400 \times 10^3 \times 500 = 200 \times 10^6 \text{ W} = 200 \text{ MW}$ [B1]

(b) Explanation: High voltage reduces the current for a given power ( $P=VI$ ). Since power loss in cables is $I^2 R$ , reducing current significantly reduces energy loss as heat. [B1]

19. (a) Calculation: $\frac{1}{R_{eq}} = \frac{1}{2} + \frac{1}{3} + \frac{1}{6} = \frac{3}{6} + \frac{2}{6} + \frac{1}{6} = \frac{6}{6} = 1$ $R_{eq} = 1 \Omega$ [M1] for formula, [A1] for answer.

20. (a) Description: The charge decreases exponentially over time as it flows through the resistor. [B1]

(b) Energy Conversion: Electrical potential energy (stored in the capacitor) is converted to thermal energy (heat) in the resistor. [B1]