Electromagnets In Bells & Relays

D. Crowley, 2008

Electromagnets In Bells & Relays

To understand how electromagnets are used in electric bells and relays

Tuesday, April 18, 2023

Wordsearch

Complete the magnets wordsearch…

Wordsearch

Electromagnets

A magnetic field is produced when an electric current flows through a coil of wire - this is the basis of the electromagnet

Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off just by closing or opening the switch…

Electromagnets How are electromagnets useful?

Many objects contain electromagnets - they are found in electric motors and loudspeakers

Very large and powerful electromagnets are used as lifting magnets in scrap yards to pick up, then drop, old cars and other scrap iron and steel

Electric Bell Electric bells like the ones used in most schools also contain an

electromagnet

A bell turns its electromagnet on-off-on-off very quickly, making the brriiinnngggg noise!

Electric Bell When the current flows through the circuit, the electromagnet

makes a magnetic field attracting the hammer

The hammer clangs the bell, and also pulls the contacts away, breaking the circuit

The electromagnet is turned off and the hammer moves back to its original position

The circuit is complete again and the cycle repeats (as long as the switch is closed)

Electric Bell

Complete the electric bell worksheet

Electric Bell

Relays

A relay is an electromagnetic switch – it allows a small current in one circuit to control a large current in another circuit (useful for machines which need large currents)

Relays

A small current in circuit 1 is used to switch on a much bigger current in circuit 2

When the small current is switched on it activates the electromagnet – attracting the iron lever to it, making it rotate

As it rotates the other end of the lever pushes the contacts together, turning the other circuit on…

Switch

Electromagnet pulls arm towards it

Contacts pushed together, turning

secondary circuit on