AQA GCSE Physics (8463), Higher tier · Magnetism and electromagnetism › Induced potential and transformers
Practise Induced potential. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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A coil of wire is connected to a sensitive centre-zero ammeter. A student pushes a bar magnet into the coil. The ammeter needle moves to the right. What is the name of this effect?
The generator effect
Explain why a potential difference is induced across the ends of the wire.
The wire moves through (cuts) the magnetic field, which induces a potential difference.
What name is given to this effect?
The generator effect (electromagnetic induction).
Give one way of inducing a potential difference across a coil of wire, using a magnet.
Move the magnet into (or out of) the coil.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
A coil of wire is connected to a sensitive centre-zero ammeter. A student pushes a bar magnet into the coil. The ammeter needle moves to the right.
(a) What is the name of this effect?[1]
(b) The student holds the magnet still inside the coil. What does the ammeter show? Tick (✓) one box.[1]
A reading of zero
A steady reading to the right
A steady reading to the left
(c) The student pulls the magnet out of the coil. Describe what happens to the ammeter needle.[1]
(d) Give one way of making the needle move further.[1]
Show the answer and mark scheme
(a)Answer: The generator effect
the generator effect / electromagnetic induction
(b)Answer: A reading of zero
(c)Answer: It moves to the left.
it moves to the left / in the opposite direction (then returns to zero)
(d)Answer: Move the magnet faster.
move the magnet faster / use a stronger magnet / use a coil with more turns
Question 2Medium7 marks
A student moves a straight wire up and down between the poles of a U-shaped magnet. The ends of the wire are connected to a sensitive voltmeter.
(a) Explain why a potential difference is induced across the ends of the wire.[2]
(b) Give two ways of increasing the induced potential difference.[2]
(c) Give one way of reversing the direction of the induced potential difference.[1]
(d) The student moves the wire along the direction of the magnetic field lines. Explain why the voltmeter reads zero.[1]
(e) The voltmeter is replaced by a sensitive ammeter, making a complete circuit. What happens when the wire is moved up and down now?[1]
Show the answer and mark scheme
(a)Answer: The wire moves through (cuts) the magnetic field, which induces a potential difference.
the wire moves relative to the magnetic field / cuts the magnetic field lines
so a potential difference is induced (the generator effect)
(b)Answer: Move the wire faster; use a stronger magnet.
move the wire faster
use a stronger magnet
use a coil of many turns / more wire in the field
(c)Answer: Move the wire the other way.
move the wire in the opposite direction / reverse the magnet (swap the poles)
(d)Answer: The wire does not cut any field lines.
the wire does not cut the field lines / the magnetic field around the wire does not change
(e)Answer: An induced current flows, reversing each time the wire changes direction.
a current is induced in the circuit (which changes direction as the wire changes direction)
Question 3Hard8 marks
A strong magnet is dropped down a vertical copper tube. It takes much longer to fall through the tube than an identical piece of unmagnetised metal. Copper is a good electrical conductor but it is not a magnetic material.
(a) Explain why the magnet falls slowly.[4]
(b) The copper tube is replaced by a plastic tube of the same size. Predict how the fall of the magnet changes. Give a reason for your answer.[2]
(c) A long, narrow slit is cut along the whole length of the copper tube. Suggest how this affects the fall of the magnet. Give a reason.[2]
Show the answer and mark scheme
(a)Answer: The falling magnet induces currents in the copper; these produce a magnetic field that opposes the magnet's motion, giving an upward force.
as the magnet falls, the magnetic field around the copper tube changes / the tube is cut by the magnet's field
a potential difference is induced in the copper, and because copper is a conductor a current is induced
the induced current produces its own magnetic field
which opposes the change that caused it, so there is an upward force on the magnet (opposing its motion)
(b)Answer: It falls freely, because no current can be induced in an insulator.
the magnet falls quickly / at the same rate as the unmagnetised metal
plastic is an insulator so no current is induced (so no opposing magnetic field)
(c)Answer: It falls faster, because the slit stops the induced currents flowing round the tube.
the magnet falls faster than in the tube without the slit
the slit stops current flowing round the tube, so the induced currents (and the opposing field) are smaller