# Uses of Electromagnetism

In this worksheet, students will learn of the uses of electromagnets, including those in generating electricity.

Key stage:  KS 4

GCSE Boards:   AQA, AQA Trilogy, AQA Synergy, OCR 21st Century, OCR Gateway, Pearson Edexcel

Difficulty level:

### QUESTION 1 of 10

Electromagnets are more useful than permanent magnets because they can be switched on and off, the strength of the magnetic field can be altered, they can easily be given the desired shape and they are cheaper to make. They are also much cooler, allowing us to make floating trains and other sci-fi stuff like that! You are living int he future now!

General uses

Huge electromagnets are used to lift cars and other heavy metal objects. The objects are dropped to the desired location by switching off the electric current and subsequently the magnet.

Electric motors (see image below) use the Motor Effect, described in the worksheet 'Magnetism and Electromagnetism', to spin a coil of wire inside a magnetic field. The speed of the motor can be changed by changing the strength of the magnet, adding more loops and changing the electric current. The direction of the motor can be changed by changing the direction of the current.

In loudspeakers (see diagram below) an alternating current that flows through the coil represents the sound wave. The force produced makes the coil move, which pulls the cone to one direction. As the direction of the current changes, the direction of the force also changes and the cone is pulled the opposite way. The forward and backward motion of the cone produces a sound wave in the air.

The pitch and loudness of the sound depends on the frequency and amplitude of the electrical signal, which affect the size of the force.

Relays work by using a small current circuit to activate an electromagnet; this pushes the soft iron armature, which brings the contacts of the large current circuit together, thus creating the output effect.

Generating electricity

Electricity can be generated in two ways:

1) Moving a wire in a magnetic field. The direction and speed of the wire determines the direction and size of the current, respectively.

2) Moving a magnet in a coil of wire. The direction and position of the poles determine the direction of the current. The speed of the magnet determines the size of the current.

Industrial processes of generating electricity involve spinning a coil of wire in a magnetic field. The current produced is called induced current. During each rotation, each side of the coil moves up and down. The change in direction results in the change of the current's direction, so the current is called an alternating current (AC).

Transformers are used in the National Grid to change the voltage of alternating current to reduce energy waste and to produce current safe for use at home. The magnetic field around the alternating current in the primary coil changes, which induces an alternating current and voltage in the secondary coil. The number of loops in the coil determine the size of the voltage (see diagram).

The size of the output voltage can be calculated with the formula in the diagram above.

Tick two reasons why electromagnets are more useful than permanent magnets.

They cannot be switched off.

They can be switched on and off.

They have a fixed shape.

They can be shaped according to the purpose of their use.

Their magnetic field is fixed.

They are expensive.

Why are electromagnets used to lift heavy objects?

The object stays fixed to the magnet.

The objects are heavy and only electromagnets can lift them.

The objects can be dropped to the desired location when the electromagnet is switched off.

Tick two ways to increase the speed of an electric motor.

Using a weaker magnet

Using a stronger magnet

Adding loops to the coil of wire

Reducing the number of loops in the wire

In a loudspeaker, what does the alternating current represent?

A sound wave

A magnetic force

A magnetic field

How is a sound wave produced in loudspeakers?

By the backward motion of the cone

By the forward motion of the cone

By the backward and forward motion of the cone

What is the purpose of an electromagnet in relays?

When it is activated, it brings together the contacts in the small circuit.

When it is activated, it brings together the contacts in the large circuit.

It creates a magnetic field.

Tick two ways in which electricity can be generated.

Moving a wire in a magnetic field

Moving a magnet in a magnetic field

Moving a magnet in a coil of wire

Moving a transformer in a relay

What is the current generated in the industry called?

Study the diagram about the direction of the induced current:

RIght Hand Rule for Induced Current

A conductor in motion through a magnetic field will generate an induced current in the conductor.

Example: AC generator.

LeFt Hand Rule for Force

A conductor carrying an electric current in a magnetic field will move because the magnetic field of the magnet will interact with the magnetic field of the current in the wire.

Example: electric motor.

Tick the option that states the correct relationship between the magnetic field and the induced current.

The induced current flows in the opposite direction of the magnetic field.

The induced current flows at a right angle to the direction of the magnetic field.

The direction of the magnetic field is shown by the second finger.

What determines the size of the voltage in a transformer?

Alternating current

Primary current

Number of loops

• Question 1

Tick two reasons why electromagnets are more useful than permanent magnets.

They can be switched on and off.
They can be shaped according to the purpose of their use.
EDDIE SAYS
Electromagnets are more useful than permanent magnets, because they can be switched on and off, the strength of the magnetic field can be altered, they can easily be given the desired shape and they are cheaper to make.
• Question 2

Why are electromagnets used to lift heavy objects?

The objects can be dropped to the desired location when the electromagnet is switched off.
EDDIE SAYS
The reason for lifting heavy objects is to move them to a specified place. It would be impossible to do that with a permanent magnet, as the objects would stay firmly attracted to it. With an electromagnet, magnetism can be switched on and off by switching the electric current on and off, respectively.
• Question 3

Tick two ways to increase the speed of an electric motor.

Using a stronger magnet
Adding loops to the coil of wire
EDDIE SAYS
The speed of an electric motor increases when a stronger magnet is used or when adding more loops to the coil of wire. This increases the artificial magnetic field in them making them more repulsive to one another. this in turn speed everything up!
• Question 4

In a loudspeaker, what does the alternating current represent?

A sound wave
EDDIE SAYS
The alternating current in loudspeakers represents sound waves. If it was a direct current then all you would get is one chirp when you turned it on and one chirp when you turned it off.
• Question 5

How is a sound wave produced in loudspeakers?

By the backward and forward motion of the cone
EDDIE SAYS
In loudspeakers an alternating current that flows through the coil represents the sound wave. The force produced makes the coil move, which pulls the cone to one direction. As the direction of the current changes, the direction of the force also changes and the cone is pulled the opposite way. The forward and backward motion of the cone produces a sound wave in the air.
• Question 6

What is the purpose of an electromagnet in relays?

When it is activated, it brings together the contacts in the large circuit.
EDDIE SAYS
When the electromagnet in the small relay circuit is activated, it brings together the contacts in the large circuit by pushing the soft iron armature.
• Question 7

Tick two ways in which electricity can be generated.

Moving a wire in a magnetic field
Moving a magnet in a coil of wire
EDDIE SAYS
Electricity can be generated by moving a wire in a magnetic field or by moving a magnet in a coil of wire. This is done in every way of generating electricity apart from solar.
• Question 8

What is the current generated in the industry called?

Induced
Induced current
EDDIE SAYS
Current produced in the industry is induced current. It means that there is not really meant to be a current there, but we are making one by moving the coil of wires in the magnetic field.
• Question 9

Study the diagram about the direction of the induced current:

RIght Hand Rule for Induced Current

A conductor in motion through a magnetic field will generate an induced current in the conductor.

Example: AC generator.

LeFt Hand Rule for Force

A conductor carrying an electric current in a magnetic field will move because the magnetic field of the magnet will interact with the magnetic field of the current in the wire.

Example: electric motor.

Tick the option that states the correct relationship between the magnetic field and the induced current.

The induced current flows at a right angle to the direction of the magnetic field.
EDDIE SAYS
Fleming's rule for induced current and magnetic fields states that the induced current flows at a right angle to the direction of the magnetic field.
• Question 10

What determines the size of the voltage in a transformer?

Number of loops
EDDIE SAYS
The number of loops in the coil determines the size of the voltage. If there are more coils on the secondary means it is a step-up transformer and less means that it is a step-down transformer.
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