## Basic electricity

1. What is the definition of capacitance?

2. What does n mean in the equation I = nAve

3. What is the definition of a volt?

4. What is the definition of electromotive force (e.m.f)?

5. What is meant by internal resistance?

6. How does the potential difference across two equal resistors connected in parallel compare with that across one of them?

7. Give a formula for the resistivity of a material.

8. Why is electricity transmitted at high voltage?

9. Explain what happens to the resistance of a wire as its temperature rises.

10. A graph is plotted of charge against time for the discharge of a capacitor. How can the current at any time be found?

11. A graph is plotted of current against time for the discharge of a capacitor. How can the charge passed be found?

12. What is meant by the breakdown potential for a capacitor?

13. What is meant by non-ohmic behaviour?

14. Give one domestic appliance that might contain a thermistor.

15. A capacitor of capacitance 0.47 μF is charged to a potential of 400V. Calculate:
(a) The energy stored in it
(b) The mean current if it discharges in 0.01s

16. Explain the difference in energy between a coulomb of charge delivered by either the mains (240V) or a car battery (12V)

17. Three resistors (10 kΩ, 10kΩ and 20 kΩ) are joined in series to a 12 V supply. What is the voltage across:
(a) One of the 10 kΩ resistors
(b) The 20 kΩ resistor

18. The filament in a light bulb gets thinner with use. What happens to its resistance as a result of this?

19. What is a free electron?

20. Why is the internal resistance of a source a useful safety factor?

21. Explain the term – negative temperature coefficient of resistance.

22. Give an example of a material that has a negative temperature coefficient of resistance

23. Give one disadvantage of laying power cables underground.

24. Define electrical resistance.

25. A 2A fuse connected to a 12V 24W lamp and is found to blow immediately the lamp is switched on. Why?