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Secondary 4 Pure Physics Practice Paper 1

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TuitionGoWhere Practice Paper - Pure Physics Secondary 4

TuitionGoWhere Practice Paper (AI)
Version: 1 of 5
Subject: Pure Physics
Level: Secondary 4 (O-Level 6091)
Paper: Electricity & Magnetism Practice Paper
Duration: 1 hour 15 minutes
Total Marks: 50

Name: ________________________
Class: ________________________
Date: ________________________

Instructions to Candidates

Write your name, class, and date in the spaces provided.
Answer all questions.
Write your answers in the spaces provided on this question paper.
You may use a calculator.
Take the acceleration of free fall, $g = 10 \text{ m/s}^2$ .
The total mark for this paper is 50.

Section A: Structured Questions (30 Marks)

Answer all questions in this section.

1. A student rubs a polythene rod with a dry cloth. The rod becomes negatively charged.
(a) Explain, in terms of electron transfer, how the rod becomes negatively charged.
[2]

(b) The charged rod is brought near a small piece of neutral paper. The paper is attracted to the rod. Explain why this attraction occurs.
[2]

2. Figure 2.1 shows a simple circuit containing a battery, a switch, a lamp, and a component X.

(Imagine Figure 2.1: A series circuit with Battery, Switch, Lamp, and Component X)

Component X is a thermistor.
(a) State how the resistance of the thermistor changes as the temperature increases.
[1]

(b) The temperature of the thermistor increases. State and explain the effect on the brightness of the lamp.
[2]

3. A transformer is used to step down the voltage from 240 V to 12 V for a laptop charger. The primary coil has 2000 turns.
(a) Calculate the number of turns on the secondary coil.
[2]

(b) The laptop draws a current of 3.0 A from the secondary coil. Assuming the transformer is 100% efficient, calculate the current in the primary coil.
[2]

4. Figure 4.1 shows a current-carrying wire placed between the poles of a U-shaped magnet. The current flows into the page.

(Imagine Figure 4.1: N pole on left, S pole on right. Wire in center with 'X' indicating current into page.)

(a) On Figure 4.1, draw an arrow to show the direction of the force acting on the wire. Label this force F.
[1]

(b) State two ways to increase the magnitude of this force.
[2]

5. A household electrical appliance has a metal casing. It is connected to the mains supply using a three-pin plug.
(a) State the colour of the insulation on the earth wire.
[1]

(b) Explain why the earth wire is connected to the metal casing of the appliance.
[2]

6. Figure 6.1 shows a coil of wire connected to a sensitive centre-zero galvanometer. A bar magnet is moved towards the coil.

(Imagine Figure 6.1: Bar magnet N-pole facing coil. Coil connected to galvanometer.)

(a) State what is observed on the galvanometer as the magnet moves towards the coil.
[1]

(b) State and explain what is observed on the galvanometer if the magnet is then held stationary inside the coil.
[2]

(c) The magnet is now pulled away from the coil quickly. Compare the deflection observed now with the deflection observed in (a).
[1]

7. Two resistors, $R_1 = 6.0 \, \Omega$ and $R_2 = 3.0 \, \Omega$ , are connected in parallel across a 12 V battery.
(a) Calculate the combined resistance of the two resistors.
[2]

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

8. An electric kettle is rated at 240 V, 2.4 kW.
(a) Calculate the current flowing through the kettle when it is operating normally.
[2]

(b) Calculate the electrical energy converted into heat energy if the kettle is switched on for 5 minutes.
[2]

9. Figure 9.1 shows the magnetic field pattern around a straight current-carrying wire.

(Imagine Figure 9.1: Concentric circles around a wire.)

(a) Describe how the spacing of the field lines changes as you move further away from the wire.
[1]

(b) What does this change in spacing indicate about the strength of the magnetic field?
[1]

10. A student investigates the relationship between the length of a wire and its resistance. The wire is made of constantan and has a uniform cross-sectional area.
(a) State the relationship between the length of the wire and its resistance.
[1]

(b) If the length of the wire is doubled while keeping the cross-sectional area constant, what happens to its resistance?
[1]

Section B: Free Response Questions (20 Marks)

Answer all questions in this section.

11. A student sets up a circuit to determine the resistance of a filament lamp. The circuit includes a battery, a switch, an ammeter, a voltmeter, the lamp, and a variable resistor.
(a) Draw the circuit diagram for this experiment. Ensure the voltmeter and ammeter are connected correctly.
[3]

(b) The student takes several readings of voltage ( $V$ ) and current ( $I$ ) and plots a graph of $V$ against $I$ . The graph is a curve that gets steeper as $V$ increases.
(i) Explain why the graph is not a straight line.
[2]

(ii) State how the resistance of the lamp changes as the voltage increases.
[1]

12. Figure 12.1 shows a simple d.c. motor. It consists of a rectangular coil ABCD placed between the poles of a magnet. The coil is connected to a split-ring commutator and carbon brushes.

(Imagine Figure 12.1: Standard DC motor diagram.)

(a) Explain the function of the split-ring commutator in the d.c. motor.
[2]

(b) State two ways to increase the speed of rotation of the motor.
[2]

(c) Explain why the coil continues to rotate in the same direction even when the plane of the coil is vertical (perpendicular to the magnetic field lines).
[2]

13. High-voltage cables are used to transmit electrical power over long distances from power stations to homes.
(a) Explain why electrical power is transmitted at high voltage.
[3]

(b) A power station generates 500 MW of power at 25 kV. This voltage is stepped up to 400 kV for transmission.
(i) Calculate the current in the transmission cables at 400 kV.
[2]

(ii) The total resistance of the transmission cables is $2.0 \, \Omega$ . Calculate the power loss in the cables.
[2]

14. A solenoid is connected to a battery and a switch. A plotting compass is placed near one end of the solenoid.
(a) When the switch is closed, the compass needle deflects. Explain why.
[2]

(b) The current in the solenoid is reversed. State what happens to the direction of the magnetic field inside the solenoid.
[1]

15. A student has three identical lamps and a battery.
(a) Draw a circuit diagram showing how the three lamps can be connected so that if one lamp breaks, the other two remain lit.
[2]

(b) Explain why this arrangement is preferred for household lighting compared to connecting the lamps in series.
[2]

End of Paper

Answers

TuitionGoWhere Practice Paper - Pure Physics Secondary 4 (Answer Key)

Version: 1 of 5
Subject: Pure Physics
Total Marks: 50

Section A: Structured Questions

1.
(a) Electrons are transferred from the cloth to the rod [1]. The rod gains excess electrons, giving it a net negative charge [1].
(b) The negative rod repels electrons in the paper to the far side [1], leaving the near side positively charged (induction). The attractive force between the rod and the near positive side is stronger than the repulsive force from the far negative side [1].

2.
(a) Resistance decreases [1].
(b) Brightness increases [1]. As temperature increases, resistance of thermistor decreases, so total circuit resistance decreases. This causes the current to increase [1], increasing the power/brightness of the lamp.

3.
(a) $\frac{N_s}{N_p} = \frac{V_s}{V_p}$
$N_s = N_p \times \frac{V_s}{V_p} = 2000 \times \frac{12}{240}$ [1]
$N_s = 100$ turns [1]

(b) $P_{in} = P_{out}$ (100% efficient)
$V_p I_p = V_s I_s$
$240 \times I_p = 12 \times 3.0$ [1]
$I_p = \frac{36}{240} = 0.15$ A [1]

4.
(a) Arrow pointing upwards (towards the top of the page) [1].
(b) Any two of:

Increase the current [1].
Use a stronger magnet (increase magnetic flux density) [1].
Increase the length of the wire in the magnetic field.

5.
(a) Green and yellow [1].
(b) If the live wire touches the metal casing, the casing becomes live [1]. The earth wire provides a low-resistance path to the ground, causing a large current to flow, which blows the fuse/trips the breaker, preventing electric shock [1].
(c) The large current generates excessive heat in the fuse wire [1]. The fuse wire melts (blows), breaking the circuit and stopping the current flow [1].

6.
(a) The needle deflects (to one side) [1].
(b) No deflection / Needle returns to zero [1]. There is no change in magnetic flux/linkage through the coil when the magnet is stationary, so no EMF is induced [1].
(c) The deflection is in the opposite direction [1].

7.
(a) $\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} = \frac{1}{6} + \frac{1}{3} = \frac{1}{6} + \frac{2}{6} = \frac{3}{6}$ [1]
$R_{total} = \frac{6}{3} = 2.0 \, \Omega$ [1]

(b) $I = \frac{V}{R} = \frac{12}{2.0}$ [1]
$I = 6.0$ A [1]

8.
(a) $P = IV \Rightarrow I = \frac{P}{V}$
$I = \frac{2400}{240}$ [1]
$I = 10$ A [1]

(b) $E = Pt$
$t = 5 \times 60 = 300$ s [1]
$E = 2400 \times 300 = 720,000$ J (or 720 kJ) [1]

9.
(a) The field lines become further apart (spacing increases) [1].
(b) The magnetic field becomes weaker [1].

10.
(a) Resistance is directly proportional to length [1].
(b) The resistance doubles [1].

Section B: Free Response Questions

11.
(a) Diagram Requirements:

Battery, switch, variable resistor, ammeter, and lamp in series [1].
Voltmeter connected in parallel across the lamp only [1].
Correct symbols used [1].

(b)
(i) As voltage/current increases, the temperature of the filament increases [1]. The increased temperature causes the metal ions to vibrate more, increasing collisions with electrons, thus increasing resistance [1].
(ii) Resistance increases [1].

12.
(a) It reverses the direction of the current in the coil every half rotation [1]. This ensures that the force on the arms of the coil always acts in the same rotational direction, allowing continuous rotation [1].
(b) Any two of:

Increase the current [1].
Use a stronger magnet [1].
Increase the number of turns on the coil.
Increase the area of the coil.

(c) At the vertical position, the plane of the coil is perpendicular to the magnetic field. The forces on the sides of the coil are pulling outwards/stretching the coil rather than turning it [1]. However, the momentum (inertia) of the rotating coil carries it past this vertical position [1], allowing the commutator to switch the current and maintain rotation.

13.
(a) Power loss in cables is given by $P_{loss} = I^2 R$ [1]. By transmitting at high voltage, the current $I$ is reduced for the same power output ( $P=IV$ ) [1]. A lower current significantly reduces the energy lost as heat in the transmission cables [1].

(b)
(i) $P = IV \Rightarrow I = \frac{P}{V}$
$I = \frac{500 \times 10^6}{400 \times 10^3} = \frac{500,000,000}{400,000}$ [1]
$I = 1250$ A [1]

(ii) $P_{loss} = I^2 R$
$P_{loss} = (1250)^2 \times 2.0$ [1]
$P_{loss} = 1,562,500 \times 2 = 3,125,000$ W (or 3.125 MW) [1]

14.
(a) When current flows, a magnetic field is produced around the solenoid [1]. This magnetic field interacts with the magnetic needle of the compass, exerting a force that causes it to align with the field lines [1].
(b) The direction of the magnetic field reverses [1].
(c) The strength of the magnetic field increases significantly [1]. Iron is a ferromagnetic material; it becomes magnetically induced, concentrating the magnetic field lines within the core [1].

15.
(a) Diagram Requirements:

Battery connected to three lamps in parallel [1].
Each lamp is on a separate branch connected across the battery terminals [1].

(b) In a parallel circuit, each lamp receives the full voltage of the supply, so they shine at full brightness [1]. If one lamp breaks (open circuit), the other branches remain complete, so the other lamps stay lit [1]. (In series, one break stops all current, and voltage is shared, making lamps dimmer).