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Solved problems for the chapter:

Electromagnetic Induction

View the theory »

Torque of a Magnetic Force

1. Current loop in a magnetic field

2. Coil in a magnetic field

3. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:electromagnetic_induction/3648/

Example 1.

The figure below shows an arrangement used to demonstrate electromagnetic induction.

When the magnet moves towards the coil of wire, the pointer on the sensitive voltmeter deflects to the right.

Explain why the pointer deflects.

Example 2.

The diagram below shows an arrangement used to demonstrate electromagnetic induction.

When the magnet moves towards the coil of wire, the pointer on the sensitive voltmeter deflects to the right.

Explain two changes that increase the deflection on the sensitive voltmeter.

Which statement about electromagnetic induction is correct?

A conductor moving parallel to magnetic field lines induces an electromotive force (e.m.f.) in the conductor.
The direction of the induced electromotive force (e.m.f.) opposes the change which produces it.
The induced current is in a direction parallel to the direction of motion producing it.
The induced electromotive force (e.m.f.) decreases when the speed of the conductor moving across the field lines increases.

A wire is moved down in a direction perpendicular to the magnetic field.

Three changes are suggested.

The speed of the movement of the wire is increased.
The magnetic field strength is decreased.
The direction of the magnetic field is reversed.

Which changes increase the electromotive force (e.m.f.) induced in the wire?

1 and 3
1 only
2 and 3
3 only

Two circuits are set up as shown. The iron rods are placed close together and are free to move.

What happens to the size of the gap at X when switch S is closed?

It decreases.
It decreases then increases.
It increases.
It does not change.

A clamp and stand hold a soft-iron bar above a bench. A coil of wire is wrapped round the soft-iron bar. The coil of wire is part of an electric circuit. The figure below shows the arrangement.

Switch S is closed. A student holds a soft-iron disc close to the bar and releases the disc. The disc becomes attached to the bar as shown in the figure above

Explain why the soft-iron disc is attracted to the soft-iron bar.

A coil is connected to a battery and a soft iron bar is hung near it.

The current is then reversed by reversing the battery connections.

How does the soft iron bar behave in the two cases?

	with the battery as shown	with the battery reversed
A	attracted to the coil	attracted to the coil
B	attracted to the coil	repelled from the coil
C	repelled from the coil	attracted to the coil
D	repelled from the coil	repelled from the coil

A student investigates electromagnetic induction. She moves the N pole of a magnet quickly towards a coil of wire. There is a reading on the galvanometer.

What can she do to get a greater reading on the galvanometer?

Hold the bar magnet stationary inside the coil.
Move the bar magnet slowly away from the coil.
Use a coil of wire with fewer turns on it.
Use a stronger bar magnet.

The diagram shows a solenoid connected to a sensitive voltmeter.

Which of the following would give a zero reading on the voltmeter?

holding the magnet stationary inside the solenoid
moving the magnet away from the solenoid
moving the magnet towards the solenoid
moving the solenoid towards the magnet

10.

An electromagnet is positioned close to a coil of wire.

The electromagnet is switched on, remains on for a short time, and is then switched off. Three statements about the pointer on the galvanometer during this sequence are given.

The pointer kicks to one side as the electromagnet is switched on.
The pointer records a steady non-zero value while the electromagnet remains switched on.
The pointer kicks to the other side as the electromagnet is switched off.

Which statements are correct?

1 and 2 only
1 and 3 only
2 and 3 only
1, 2 and 3

11.

A teacher demonstrates electromagnetic induction using the apparatus as shown below.

The teacher pulls the magnet down until one end is inside the coil. The teacher then releases the magnet. The magnet moves up and down repeatedly. As it moves, one end of the magnet enters and leaves the coil.

Describe and explain the readings on the centre-zero millivoltmeter as the magnet enters and leaves the coil.

12.

A student is experimenting with electromagnetic effects.

Describe an experiment, using any standard laboratory equipment, to demonstrate electromagnetic induction. You may draw a diagram.

13.

When a metal wire moves up, cutting a magnetic field, an electromotive force (e.m.f.) is induced across the wire. Which change affects the magnitude of the induced e.m.f.?

moving the wire down at the same speed
moving the wire up at a faster speed
using a thicker wire
using a wire made from a different metal

14.

An electromagnet consists of a solenoid X that is made of copper wire. The solenoid contains an iron core. The electromagnet is inside a second solenoid Y.

Describe and explain what happens in solenoid Y when solenoid X is connected to an alternating current (a.c.) power supply.

15.

A student wishes to demonstrate electromagnetic induction. He has a magnet and connecting wires. Which other apparatus does he need?

16.

The figure below shows a magnet held just below a vertical coil connected to a galvanometer.

The magnet is released.

State any effect on the galvanometer.
State any effect on the magnetic field produced by the coil.

17.

Which statement about electromagnetic induction is correct?

A strong magnet that is held stationary near a stationary conductor causes a greater effect than a weak magnet.
The effect occurs when a magnet and a conductor are both moved with the same speed and in the same direction.
The effect occurs when a magnet is moved away from a nearby conductor.
The effect only occurs when a magnet is moved towards a conductor.

18.

A student makes an electromagnet. He places an iron rod inside a coil of wire and connects the coil to a d.c. power supply as shown below.

The switch is closed so there is a current in the coil. The S pole of a bar magnet is placed near to each end of the iron rod in turn. Suggest what happens at each end of the iron rod and give a reason for your predictions.

Suggestions ................................................................

Reason ...................................................................

19.

Two soft-iron rods are placed end-to-end inside a coil. The coil is connected to a battery.

The connections from the battery to the coil are now reversed. What happens to the soft- iron rods in each case?

	battery connections as shown	battery connections reversed
A	Attract	Attract
B	Attract	Repel
C	Repel	Attract
D	Repel	Repel

20.

A magnet is suspended from a spring so that it can move freely inside a stationary coil. The coil is connected to a sensitive centre-zero galvanometer.

The magnet repeatedly moves slowly up and down. What does the galvanometer show?

a constantly changing reading
a steady reading to the left
a steady reading to the right
a steady reading of zero