# AQA P3.3 Keeping things moving

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 Author: HLHSscience ID: 213218 Filename: AQA P3.3 Keeping things moving Updated: 2013-05-03 13:52:15 Tags: AQA Physics Folders: Description: AQA P3.3 Keeping things moving Show Answers:

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1. What sort of field is produced when a current flows through a wire
• A magnetic field
2. What is produced when a current flows through a wire in a magnetic field
• A force. This is called the motor effect.
•
3. How can the size of the force produced by the motor effect be increased?
• Increasing the strength of the magnetic field,
• Increasing the size of the current
4. In Flemings left-hand rule, what does the second finger represent?
• Current ( SeCond)
5. In Flemings left-hand rule, what does the first finger represent?
• Magnetic Field (First)
6. In Flemings left-hand rule, what does the thumb represent?
• Thrust (Thumb), or Movement (ThuMb) (both mean the same thing!)
7. How can the direction of the force produced by the motor effect be reversed?
• Changing the direction of the current, or
• Changing the direction of the magnetic field
8. What are the 3 ways that the strength of an electromagnet can be increased?
• More turns of wire in the coil,
• increasing the current,
• adding an iron core inside the coil
9. Name some uses of electromagnets
• Separating steel and iron from other metals,
• moving heavy pieces of iron and steel in a scrapyard,
• loudspeaker coils,
• relays,
• circuit breakers
10. What is a relay used for?
• Using a low pd circuit to switch on a high pd circuit. (This makes it much safer to use)
11. What does a circuit-breaker do?
• Used to switch off current in a circuit if the current is too high (usually because of a fault)
12. What is produced when a wire is moved in a magnetic field?
A potential difference is induced in the wire. (This can be used to make current flow)
13. What does an electrical transformer do?
Changes the potential difference (voltage).

A step-up transformer increases the pd. A step-down transformer reduces the pd.
14. What are the two coils called in a transformer?
• Primary and secondary coils
15. What are the 3 components of a transformer?
• Primary coil,
• Secondary coil,
• Iron core
16. In the equation

what does Ns represent?
The number of turns in the secondary coil
17. Step-up transformers induce a larger pd in the secondary coil (output) than the primary coil (input). How can this be when the law of conservation of energy states that energy cannot be created or destroyed?
Step-up transformers increase the pd in the secondary coil but also decrease the current.

• As Power = voltage x current,
• the overall power (and hence energy) remains the same.
18. Transformers are less than 100% efficient. Where does the wasted energy go?
• Heat
19. Switch-mode transformers are more modern versions of transformers and use electronic circuits inside them. What are the advantages of this type of transformer?
• Smaller,
• lighter,
• use very little power when no load is applied (such as when a mobile battery is left on charge but is fully charged)

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