1. Electromagnets In Bells & Relays D. Crowley, 2008

2. Electromagnets In Bells & Relays  To understand how electromagnets are used in electric bells and relays Wednesday, May 20, 2015

3. Wordsearch  Complete the magnets wordsearch…

4. Wordsearch

5. 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…

6. 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

7. 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!

8. 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)

9. Electric Bell  Complete the electric bell worksheet

10. Electric Bell

11. 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)

12. 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