Electromagnetic InductionEdexcel GCSE Physics: Topic test

20 questions, 54 marks

Edexcel GCSE Physics

Electromagnetic Induction topic test

Total 54 marks

Name

Class

Date

1
A cyclist fits a small dynamo to her bicycle wheel. The dynamo consists of a permanent magnet mounted close to a coil of wire; as the wheel turns, the magnet rotates past the coil, inducing a current that powers the bicycle's front lamp. When the cyclist pedals faster, the lamp glows more brightly.
(a)
What causes a current to be induced in the coil as the bicycle wheel turns?
[1 mark]
AThe magnet moving relative to the coil changes the magnetic field through the coil
BThe coil becomes permanently magnetised by contact with the magnet
CFriction between the wheel and the axle generates the current directly
DThe coil's resistance decreases as the wheel spins faster
(b)
Why does the bicycle lamp glow more brightly when the cyclist pedals faster?
[1 mark]
APedalling faster reduces the resistance of the lamp's filament
BPedalling faster increases the rate of change of magnetic field through the coil, inducing a larger potential difference
CPedalling faster increases the strength of the permanent magnet
DPedalling faster reduces the frequency of the induced current, increasing its size
(c)
Explain why the current produced by the bicycle dynamo is alternating current rather than direct current.
[2 marks]
Total for question 1: 4 marks
2
A pair of over-ear headphones contains, in each earpiece, a small coil of wire attached to a thin flexible diaphragm and positioned inside a permanent magnetic field. An alternating current representing an audio signal from a phone is fed into the coil.
(a)
What causes the diaphragm in the headphone earpiece to move back and forth as the audio signal plays?
[1 mark]
AThe diaphragm becomes magnetised and is attracted to the permanent magnet
BThe changing current heats the coil, causing it to expand and contract
CThe alternating current in the coil experiences a varying force from the permanent magnetic field, pushing the coil and diaphragm back and forth
DSound waves from the phone directly push the diaphragm
(b)
Why must the current supplied to the headphone coil be alternating rather than direct for it to reproduce sound?
[1 mark]
AA direct current would demagnetise the permanent magnet almost immediately
BA direct current cannot pass through a coil of wire at all
CA direct current would make the diaphragm vibrate faster than any alternating current could
DA direct current would push the diaphragm to one fixed position and hold it there, producing no vibration and no sound
(c)
Explain how the vibrating diaphragm produces a sound wave that matches the original audio signal.
[2 marks]
Total for question 2: 4 marks
3
An emergency hand-crank torch contains a small generator: turning the crank handle rotates a coil of wire inside a strong permanent magnetic field, inducing a current that charges an internal battery. A warning label states that turning the crank handle faster produces a larger charging current.
(a)
Explain, in terms of the induced potential difference, why turning the crank handle faster produces a larger charging current.
[3 marks]
(b)
Using the factors that affect the size of an induced potential difference, describe four separate changes to the crank generator's design that would increase the current it produces for the same cranking speed.
[4 marks]
Total for question 3: 7 marks
4
A small wind turbine on an off-grid farm is being designed to charge a bank of storage batteries. The turbine's rotor turns a coil of wire inside a magnetic field to generate electricity. The engineer must decide whether to fit an alternator, which produces alternating current and would need a rectifier circuit to convert its output to direct current for the batteries, or a dynamo, which uses a split-ring commutator to produce direct current directly.
(a)
Explain the difference in construction and operation between an alternator and a dynamo, and explain why each produces the type of current (alternating or direct) that it does.
[6 marks]
(b)
Evaluate the choice between fitting an alternator with a rectifier circuit and fitting a dynamo directly, for this off-grid, battery-charging wind turbine application.
[6 marks]
Total for question 4: 12 marks
5
A laptop charger contains a small step-down transformer. The primary coil, which has 920 turns, is connected to the UK mains alternating supply of 230 V. The secondary coil has 40 turns and supplies a lower alternating voltage to the laptop's internal circuitry, which then converts it to direct current.
(a)
What causes a changing current in the primary coil to induce a voltage in the secondary coil, even though the two coils are not directly connected by wires?
[1 mark]
AThe changing current in the primary coil produces a changing magnetic field that links with the secondary coil, inducing a potential difference in it
BElectrons flow directly from the primary coil across a small air gap into the secondary coil
CThe iron core becomes an electrical conductor and carries current from one coil to the other
DHeat generated in the primary coil is conducted to the secondary coil and generates a voltage there
(b)
Using the turns-ratio equation, what is the output (secondary) voltage of this transformer?
[1 mark]
A20 V
B10 V
C5290 V
D230 V
(c)
Explain why this transformer would not work if the primary coil were connected to a direct current supply instead of an alternating supply.
[2 marks]
Total for question 5: 4 marks
6
An electric toothbrush charges wirelessly: when placed on its charging base, a coil inside the base carries an alternating current and is positioned close to, but not touching, a second coil inside the toothbrush handle. This induces an alternating current in the toothbrush's coil, which is then converted to direct current to charge its internal battery.
(a)
Why is it essential that the current in the base's coil is alternating rather than direct for the toothbrush to charge?
[1 mark]
AAn alternating current travels further through air than a direct current
BA direct current cannot flow through a coil of wire
COnly a changing current produces a changing magnetic field, which is needed to induce a current in the toothbrush's coil
DA direct current would be too weak to pass through the plastic casing of the toothbrush
(b)
What happens to the current induced in the toothbrush's coil if the handle is placed slightly further away from the base than normal?
[1 mark]
AThe induced current increases, because the coils then act more like an aerial
BThe induced current stays exactly the same regardless of the distance between the coils
CThe induced current reverses direction because the field lines spread out further
DThe induced current decreases, because the changing magnetic field reaching the toothbrush's coil is weaker
(c)
Explain why the two coils do not need to be connected by wires, or even touch each other, for energy to be transferred from the base to the toothbrush.
[2 marks]
Total for question 6: 4 marks
7
A step-down transformer at a local substation reduces a transmission voltage of 11 000 V to a domestic supply voltage of 230 V for a housing estate. The transformer can be assumed to be 100% efficient. At one moment, a current of 4.6 A flows from the transformer into the local network on the 230 V (secondary) side.
(a)
Calculate the current flowing into the transformer on the 11 000 V (primary) side at this moment. Show your working.
[3 marks]
(b)
Using the equation P = V x I, explain why transmitting electrical power at 11 000 V rather than at 230 V means a much smaller current is needed to deliver the same amount of power, and explain why this smaller current reduces the energy wasted in the transmission cables.
[4 marks]
Total for question 7: 7 marks
8
An energy company is connecting a remote island to the mainland's electrical grid using a long undersea cable. The mainland grid delivers power to the cable via a step-up transformer, and a step-down transformer near the island reduces the voltage again before it is distributed to island homes. As an alternative, the island could instead generate its own electricity locally using diesel generators, avoiding the undersea cable and transformers altogether.
(a)
Explain, in terms of current, resistance and power, why transmitting electrical power along the undersea cable at a high voltage, using step-up and step-down transformers at each end, results in less energy being wasted than transmitting the same power at a low voltage.
[6 marks]
(b)
Evaluate the advantages and disadvantages of connecting the island to the mainland grid via the undersea cable, compared with the island generating its own electricity locally using diesel generators.
[6 marks]
Total for question 8: 12 marks

End of questions