P15.3 Electromagnets in devices

Question 1

What are the 4 examples of electromagnets?

Answer 1

A circuit break
Scrapyard crane
Electric bell
Relay

Question 2

How does a scrapyard crane work?

Answer 2

Scrap vehicles are lifted in a scrap yard using powerful electromagnets attached to cranes

Question 3

How does a scrapyard crane lift objects up?

Answer 3

The steel frame of a vehicles sticks to the electromagnet when current passes through the coil of the electromagnet
When the current is switched off, the vehicle frame falls off the electromagnet

Question 4

How does a circuit breaker work?

Answer 4

A circuit breaker is a switch in series with an electro magnet
Switch is held closed by a spring
When current is too large the switch is pulled open by the electromagnet and stays open until it is reset manually

Question 5

How does an electric bell work?

Answer 5

When an electric bell is connected to a battery - the iron armature is pulled onto the electromagnet
This opens the make-and-break switch, and the electromagnet is switched off
Because of this the armature springs back and the make-and-break switch closes again
The whole cycle repeats itself

Question 6

What is the purpose of a relay?

Answer 6

To switch an electrical machine on or off

Question 7

How does a relay work?

Answer 7

A small current through the coil of the electromagnet magnetises the iron core
Which then pulls the armature onto the electromagnet
This closes the switch gap and switches the machine on

Question 8

Why are relays helpful?

Answer 8

A small current in the coil can switch on a machine with a much bigger current