Electricity and MagnetismCambridge IGCSE Physics: Topic test

20 questions, 54 marks

Cambridge IGCSE Physics

Electricity and Magnetism topic test

Total 54 marks

Name

Class

Date

1
A student holds a bar magnet close to a small pile of unmagnetised soft iron filings and, separately, close to a small pile of unmagnetised plastic beads.
(a)
What happens to the iron filings near the magnet?
[1 mark]
AThey are attracted to the magnet, becoming induced (temporary) magnets while in the field
BThey are repelled from the magnet
CNothing happens, since iron is not a magnetic material
DThey become permanently magnetised and stay magnets forever afterwards
(b)
What happens to the plastic beads near the magnet?
[1 mark]
AThey are attracted, since all materials are affected by magnetism
BNothing happens, since plastic is a non-magnetic material
CThey are repelled
DThey become permanently magnetised
(c)
State the difference between the properties of a temporary magnet made from soft iron and a permanent magnet made from steel.
[2 marks]
Total for question 1: 4 marks
2
A student sets up a circuit to investigate the resistance of a length of nichrome wire. With the ammeter reading a current of 0.40 A through the wire, the voltmeter connected across the wire reads a potential difference of 3.2 V.
(a)
What is the resistance of the wire?
[1 mark]
A1.28 ohm
B0.125 ohm
C8.0 ohm
D3.6 ohm
(b)
The student then uses a wire of the same material but twice the length and the same cross-sectional area. How does the resistance of this longer wire compare with the original?
[1 mark]
AIt is half as much
BIt is the same
CIt is four times as much
DIt is twice as much
(c)
State how the resistance of a wire depends on its cross-sectional area, and use this to state what would happen to the wire's resistance if a wire of double the cross-sectional area, but the same length and material, were used instead.
[2 marks]
Total for question 2: 4 marks
3
In a circuit, a 6.0 V battery is connected to two resistors, of resistance 4.0 ohm and 8.0 ohm, connected in series with each other and with an ammeter.
(a)
Calculate the combined resistance of the two resistors, and the current flowing in the circuit.
[3 marks]
(b)
The two resistors are then reconnected in parallel with each other across the same 6.0 V battery. Calculate the combined resistance of the two resistors in this parallel arrangement, and state, with a reason, how the total current drawn from the battery in the parallel arrangement compares with the current in the series arrangement.
[4 marks]
Total for question 3: 7 marks
4
A household electric kettle is labelled '230 V, 2.5 kW'. The kettle is connected to the 230 V mains supply using a cable fitted with a plug that contains a fuse, and the manufacturer must choose an appropriate fuse rating for the plug from the standard ratings available: 3 A, 5 A and 13 A.
(a)
Calculate the normal operating current of the kettle, and use your answer to determine which of the standard fuse ratings should be fitted in the plug, explaining why a fuse with too low a rating, and a fuse with too high a rating, would each be unsuitable.
[6 marks]
(b)
State why the plug's outer casing is made from an electrical insulator, and explain the purpose of the earth wire in the kettle's mains cable, describing what happens if a fault causes the kettle's metal casing to become live while the earth wire is correctly connected.
[6 marks]
Total for question 4: 12 marks
5
A student rubs a plastic rod with a dry cloth in a laboratory. After rubbing, the rod is found to be negatively charged, and it attracts small pieces of paper when held close to them.
(a)
What has happened to the plastic rod to give it a negative charge?
[1 mark]
AIt has gained electrons from the cloth
BIt has lost electrons to the cloth
CIt has gained protons from the cloth
DIt has lost protons to the cloth
(b)
What charge does the cloth now carry, and why?
[1 mark]
ANegative, because it has also gained electrons
BPositive, because it has lost electrons to the rod
CNegative, because it has lost protons
DNo charge, because charge cannot be created
(c)
State how a conductor differs from an insulator, using a simple electron model, and use this to explain what would happen differently if the charged rod were held close to a piece of metal instead of a piece of plastic.
[2 marks]
Total for question 5: 4 marks
6
An electronics hobbyist winds insulated wire into a long solenoid (coil) and connects it to a d.c. power supply, investigating the magnetic field produced when a current flows through the solenoid.
(a)
How does the magnetic field pattern outside a current-carrying solenoid compare with the field pattern outside a bar magnet?
[1 mark]
AThey are completely different in shape
BThe solenoid's field has no pattern outside it
CThe solenoid's external field pattern closely resembles that of a bar magnet
DOnly the bar magnet produces a magnetic field
(b)
What happens to the strength of the magnetic field produced by the solenoid if the current through it is increased?
[1 mark]
AThe field strength decreases
BThe field strength stays the same
CThe field direction reverses
DThe field strength increases
(c)
Describe how the hobbyist could use a plotting compass to find the direction of the magnetic field around the solenoid, and state what would happen to the direction of the field if the direction of the current through the solenoid were reversed.
[2 marks]
Total for question 6: 4 marks
7
A step-down transformer at a local substation has 4000 turns on its primary coil and 200 turns on its secondary coil. The primary coil is connected to an alternating supply of 11000 V.
(a)
Calculate the secondary voltage of this transformer.
[3 marks]
(b)
Assuming the transformer is 100% efficient and the current in the secondary coil is 80 A, calculate the current in the primary coil, and explain, using the equation for transformer efficiency, why the primary current is smaller than the secondary current in this step-down transformer.
[4 marks]
Total for question 7: 7 marks
8
A simple demonstration electric motor consists of a rectangular coil of wire, carrying a current, mounted between the poles of a permanent horseshoe magnet, with a split-ring commutator and brushes allowing continuous rotation. Each side of the coil, of length 0.080 m, carries a current of 2.5 A in a magnetic field of flux density 0.40 T, directed perpendicular to the current.
(a)
Calculate the force on one side of the coil due to the magnetic field, describe how you would determine the direction of this force, and explain how the forces on the two opposite sides of the coil combine to produce a turning effect (a torque) on the coil.
[6 marks]
(b)
Explain the purpose of the split-ring commutator in this motor, describing what would happen to the coil's rotation if the commutator were not present, and state two ways the turning effect (torque) produced by the motor could be increased.
[6 marks]
Total for question 8: 12 marks

End of questions