O Level Physics Practice Paper 1

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O-Level Physics Quiz - Electricity Magnetism

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 45

Duration: 60 Minutes
Total Marks: 45

Instructions:

• Answer all questions.
• Show all necessary working for calculation questions.
• Use 2 or 3 significant figures for your final answers.
• Use the following constants where applicable: $g = 10\text{ m/s}^2$.

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Section A: Basic Concepts and Calculations (Questions 1–8)

1. Define the term electromotive force (e.m.f.) of a cell. [1]
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2. A charge of $12\text{ C}$ passes through a conductor in $4\text{ s}$. Calculate the current flowing through the conductor. [1]
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3. A lamp is rated at $12\text{ W}$ and $6\text{ V}$. Calculate the resistance of the lamp. [2]
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4. Two resistors, $4\text{ }\Omega$ and $6\text{ }\Omega$, are connected in parallel. Calculate the equivalent resistance of the combination. [2]
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5. Explain why the resistance of a filament lamp increases as the current passing through it increases. [2]
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6. A $12\text{ V}$ battery is connected to a $3\text{ }\Omega$ resistor and a $6\text{ }\Omega$ resistor in series. Calculate the total resistance of the circuit. [1]
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7. In the circuit described in Question 6, calculate the current flowing through the $6\text{ }\Omega$ resistor. [2]
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8. State the difference between a conductor and an insulator in terms of electron flow. [1]
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Section B: Circuit Analysis and Applications (Questions 9–15)

9. A circuit contains a $10\text{ V}$ supply and two resistors in parallel: $R_1 = 20\text{ }\Omega$ and $R_2 = 30\text{ }\Omega$. (a) Calculate the total resistance of the circuit. [2]
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   (b) Calculate the current flowing through $R_1$. [2]
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10. A voltmeter is connected across a $10\text{ }\Omega$ resistor and shows a reading of $2.5\text{ V}$. Calculate the current flowing through the resistor. [2]
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11. Describe the function of a potential divider circuit. [2]
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12. A thermistor is used in a circuit to detect temperature changes. (a) State how the resistance of an NTC thermistor changes as temperature increases. [1]
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    (b) Explain how this can be used to trigger an alarm when a room becomes too hot. [2]
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13. An LDR is placed in a potential divider. How does the output voltage across the LDR change when the light intensity increases? Explain your answer. [3]
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14. A $240\text{ V}$ electric kettle is rated at $2.4\text{ kW}$. Calculate the current flowing through the kettle when it is operating at full power. [2]
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15. State two safety features used in domestic electrical wiring to prevent electric shocks. [2]
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Section C: Magnetism and Electromagnetism (Questions 16–20)

16. Describe the pattern of the magnetic field lines around a bar magnet. [2]
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17. A straight wire carries a current flowing vertically upwards. Use the Right-Hand Grip Rule to describe the direction of the magnetic field lines around the wire. [2]
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18. A current-carrying conductor is placed in a uniform magnetic field. (a) State the rule used to determine the direction of the force acting on the conductor. [1]
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    (b) State two ways to increase the magnitude of the force acting on the conductor. [2]
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19. Explain the role of the split-ring commutator in a D.C. motor. [3]
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20. A transformer has 200 turns on the primary coil and 1000 turns on the secondary coil. If the input voltage is $240\text{ V}$, calculate the output voltage. [3]
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Answer Key - O-Level Physics Quiz (Electricity Magnetism)

Qn	Answer	Marks	Marking Notes
1	The work done by the source in driving a unit charge around a complete circuit.	1	Must mention "work done" and "unit charge".
2	$I = Q/t = 12/4 = 3\text{ A}$	1	Correct value and unit.
3	$R = V^2/P = 6^2 / 12 = 36/12 = 3\text{ }\Omega$	2	1 mark for formula/substitution, 1 for answer.
4	$1/R = 1/4 + 1/6 = (3+2)/12 = 5/12 \rightarrow R = 12/5 = 2.4\text{ }\Omega$	2	1 mark for method, 1 for answer.
5	As current increases, temperature of the filament increases. This causes ions in the metal to vibrate more, increasing collisions with electrons, thus increasing resistance.	2	Must link temperature $\rightarrow$ vibration/collisions $\rightarrow$ resistance.
6	$R_{total} = 3 + 6 = 9\text{ }\Omega$	1	Correct sum.
7	$I = V/R_{total} = 12/9 = 1.33\text{ A}$	2	1 mark for $12/9$, 1 for $1.33\text{ A}$.
8	Conductors allow electrons to flow freely; insulators strongly resist the flow of electrons.	1	Clear distinction.
9a	$1/R = 1/20 + 1/30 = (3+2)/60 = 5/60 \rightarrow R = 12\text{ }\Omega$	2	1 mark for method, 1 for answer.
9b	$I_1 = V/R_1 = 10/20 = 0.5\text{ A}$	2	1 mark for substitution, 1 for answer.
10	$I = V/R = 2.5/10 = 0.25\text{ A}$	2

| 11 | A circuit that splits the input voltage into two or more output voltages based on the ratio of resistances. | 2 | Mention "splitting voltage" and "resistance ratio". |
| 12a | The resistance decreases. | 1 | Correct direction of change. |
| 12b | As temperature rises, thermistor resistance drops, increasing the voltage across the other component (or the thermistor itself depending on setup), which triggers a relay/alarm. | 2 | Link resistance drop to voltage change. |
| 13 | Output voltage across LDR decreases. As light intensity increases, LDR resistance decreases, meaning it takes a smaller share of the total voltage. | 3 | 1 mark for "decreases", 2 for explanation of resistance/voltage share. |
| 14 | $I = P/V = 2400 / 240 = 10\text{ A}$ | 2 | 1 mark for conversion to Watts, 1 for answer. |
| 15 | Earth wire (grounding) and Circuit breakers/Fuses. | 2 | 1 mark for each valid feature. |
| 16 | Lines emerge from the North pole, curve around, and enter the South pole. | 2 | Must mention direction (N to S) and shape. |
| 17 | The magnetic field lines form concentric circles around the wire, with the direction being anticlockwise (when viewed from above). | 2 | Mention circles and correct direction. |
| 18a | Fleming's Left-Hand Rule. | 1 | Correct name. |
| 18b | Increase the current; Increase the strength of the magnetic field. | 2 | 1 mark for each. |
| 19 | It reverses the direction of the current in the coil every half turn, ensuring the force always acts in the same rotational direction to keep the motor spinning. | 3 | Mention current reversal and continuous rotation. |
| 20 | $V_s/V_p = N_s/N_p \rightarrow V_s = 240 \times (1000/200) = 240 \times 5 = 1200\text{ V}$ | 3 | 1 mark for formula, 1 for substitution, 1 for answer. |