1. Magnetism and Electricity (II)
S3 Physics - 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

2. Use an ammeter. Place it in series.
What do you use to measure current and how do you place it in a circuit?
answer
Use an ammeter.
Place it in series.

3. 2. What do you use to measure voltage and how do you place it in a circuit?
answer
Use a voltmeter.
Place it in parallel.

4. 3. How is resistance related to current?
answer
As the resistance increases…
the current decreases.

5. 4. What is the unit of resistance?
answer
Ohms (Ω)

6. This is used in dimmer switches, volume controls etc…
5. What could you use to alter the current in a circuit? Give an application.
answer
A variable resistor.
This is used in dimmer switches, volume controls etc…

7. The electrical energy is converted to heat energy.
6. What happens to electrical energy when there is resistance in a wire?
answer
The electrical energy is converted to heat energy.

8. A kettle, toaster, electrical heater.
7. Give an example of where we use electrical energy being converted to heat energy.
answer
A kettle, toaster, electrical heater.

9. 8. How does a thermistor work?
answer
Its resistance varies with temperature

10. 9. What type of resistor might be controlled using e.g. sunlight?
answer
A light dependant resistor

11. What is electrical power?
answer
The rate at which electrical energy is converted into other forms.

12. 11. How does a switch control a series circuit?
answer
All switches must be closed in order for a a series circuit to operate.

13. 12. What’s the difference between a series and a parallel circuit?
answer
Series circuits have one path, parallel circuits have parallel branches.

14. 13. What is observed when a metal object is brought close to a charged Van de Graaf dome? Explain why?
answer
A spark. The Van de Graaf dome is positively charged. Negative charge moves from the metal object to the dome through the electric field.

15. 14. Match the correct fuse to each appliance. (3, 7 or 13 A)
answer
Appliance
Power rating
Fuse
Washing machine
Lamp
Hair dryer
13A 3A 7A

16. 15. How does an earth wire work?
answer
By providing an easy path for electricity to flow to ground.

17. 16. Why do plastic cased appliances not require an earth wire?
answer
Because they are DOUBLE INSULATED. This means that there is no risk of electrocution from the casing.

18. 17. Why are household circuits in parallel?
answer
This means that each appliance receives the full voltage AND that other appliances remain on when you switch one off.

19. 18. What is a ring circuit? Why is it an advantage to use in a house?
answer
It is a parallel circuit with more than one path to each socket.
Thinner cables can be used since there is less current.

20. Breakers can be reset and used again.
19. How does a mains fuse work? What is the difference between a mains fuse and a circuit breaker?
answer
A mains fuse protects the mains wiring by breaking if too large a current is drawn.
A breaker is an automatic switch which will trigger when too large a current is drawn.
Breakers can be reset and used again.

21. 20. How is an electromagnet turned into a magnet?
answer
By flowing a current through the coil

22. 21. How does a fuse act as a safety device?
answer
It melts if the current is too high.