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magnets and electromagnets lesson 6

Transcript of Magnets L6

• 1.Electromagnets Target To know electromagnets are used in relays, bells and loudspeakers. Friday 30 January 2015

2. Relays A relay is a type of switch. It allows a small current in one circuit to control a larger current in another circuit. Notes 3. Bells use electromagnets: This is an electric bell you cannot see the inside working parts but you know it contains an electromagnet, a power source (cell) and electrical leads. Try to work out how these are arranged to make the bell work. 4. Bells use electromagnets: Hint 1. There is a cell and an on/off switch. 5. Bells use electromagnets: Hint 2. There an electromagnet. This one has a horseshoe shaped electromagnet. 6. Bells use electromagnets: Hint 3. The arm of the gong has a piece of iron attached. It is attracted to the electromagnet when it is on. 7. Bells use electromagnets: Hint 4. The arm of the gong also has a contact switch attached. As the gong strikes it switched the electromagnet off. Then it springs back to switch it on again. This process repeats itself as the bell rings. 8. How a bell works. When the electricity is turned on, the iron core and coil of wire becomes an electromagnet. It then pulls the metal connected to the bell towards it. This pulls the hammer onto the bell (it rings) AND disconnects the circuit. Which turns off the electromagnet. The metal bar returns its original position. This completes the circuit again and the electromagnet switches on again. 9. Loudspeakers and how they work. The next slide shows two designs of loudspeakers. They contain a permanent magnet which is attracted and repelled by a variable electromagnet. The electromagnet is attached to a cardboard cone which vibrates to make variable sounds. 10. The electric bell. How can the sound of the bell be made: (a)Louder? (b)Higher frequency? 11. The reed switch. Write a text message to a friend to explain how a reed switch works? No more than 30 words! 12. Car starter motor. Why is it advisable for a car to have a relay switch attached to the starter motor?