CIE iGCSE Co-Ordinated Science P4.5.3 Magnetic effect of current Exam Style Questions Paper 4
Question
(a) Fig. 9.1 represents a straight piece of wire carrying a current passing through a sheet of paper.
(i) On Fig. 9.1, draw two field lines to show the shape and direction of the magnetic field around the wire.
▶️Answer/Explanation
The magnetic field lines should be concentric circles around the wire, with the direction of the field determined by the right-hand rule (thumb points in the direction of current, fingers curl in the direction of the magnetic field).
(ii) State what effect reversing the direction of the current would have on the magnetic field.
▶️Answer/Explanation
Reversing the direction of the current would reverse the direction of the magnetic field lines. The field lines would still be concentric circles, but their direction would be opposite to the original.
(b) Fig. 9.2 shows the wire placed into the magnetic field of a permanent magnet.
(i) State the direction of the force acting on the wire.
▶️Answer/Explanation
The force acting on the wire is perpendicular to both the direction of the current and the magnetic field. Using Fleming’s Left-Hand Rule, the force would be directed upwards.
(ii) Suggest two changes that would increase the size of the force acting on the wire.
▶️Answer/Explanation
1. Increasing the current flowing through the wire.
2. Increasing the strength of the magnetic field.
(c) Fig. 9.3 shows an electric motor.
(i) The following statements explain what causes the coil in Fig. 9.3 to rotate.
The statements are in the wrong order.
A A current flows through the coil.
B The coil experiences a force and starts to spin.
C The power supply applies a potential difference across the coil.
D This causes a magnetic field to be induced around the coil.
E This interacts with the permanent magnetic field.
Arrange the statements into the correct order.
▶️Answer/Explanation
The correct order is:
C → A → D → E → B
C: The power supply applies a potential difference across the coil.
A: A current flows through the coil.
D: This causes a magnetic field to be induced around the coil.
E: This interacts with the permanent magnetic field.
B: The coil experiences a force and starts to spin.
(ii) On Fig 9.3, label the split-ring commutator with a cross (X).
▶️Answer/Explanation
The split-ring commutator should be labeled with a cross (X) at the point where the coil connects to the external circuit.
(iii) Describe how the split-ring commutator allows the coil to keep on turning.
▶️Answer/Explanation
The split-ring commutator reverses the direction of the current in the coil every half turn, ensuring that the force acting on the coil always remains in the same direction, allowing the coil to continue rotating.
(d) A simple a.c. generator produces an alternating voltage.
Fig 9.4 shows how the voltage from the generator varies with time in the form of a wave.
(i) On Fig. 9.4, draw a double-headed arrow (↔) to show the time taken for the coil in the generator to complete one full rotation.
▶️Answer/Explanation
The double-headed arrow should span the time period of one complete cycle of the wave, indicating the time taken for the coil to complete one full rotation.
(ii) The size of the voltage from the generator is indicated by the amplitude of the wave in Fig. 9.4. On Fig. 9.4, draw the voltage output of the generator with a smaller voltage.
▶️Answer/Explanation
Draw a sine wave with a smaller amplitude (height) compared to the original wave, indicating a smaller voltage output.