1. Why might a good electrical conductor also be a good thermal conductor?
2. Comment on a variety of sources of electricity as a means of powering a city.
3. Calculate the current flowing in a copper wire of cross-sectional area 3x10-7m2 if the drift velocity is 0.25 mms-1.
4. Calculate the drift velocity in a silver wire of cross- sectional area 1.5x10-7m2 if a current of 30 mA flows through it.
5. Calculate how much electrical energy is supplied by a 12V battery when:
(a) a charge of 2000C passes through it
(b) a current of 3.5A flows from it for 25s
6. How much energy is drawn from a 12V car battery if it is used to supply 220A for 2s to the starter motor.
7. You have five 1.5V cells. Explain how you would connect them to give:
(a) the highest output potential
(b) a given current for the longest possible time
(c) an output potential of 4.5V
8. 20 identical light bulbs are connected in series across a 240V d.c supply.
(a) what is the p.d across each bulb
(b) what is the potential at the join of the second and third bulbs from the negative terminal?
9. If two cells, one of 4.5V and the other of 3V are connected in parallel what is the p.d across the junctions between them?
10. Calculate the current through the following resistors:
(a) 100Ω connected to 240V
(b) 4700Ω connected to 24V
(c) 10kΩ connected to 3V
(d) 2.5MΩ connected to 30V
11. What is the resistance of the following?
(a) a torch bulb that draws 0.25 A from a 12V supply
(b) an immersion heater that draws 10 A from a 240V supply
12. What is meant by:
(a) the EMF of a cell
(b) the internal resistance of a cell
13. How does the internal resistance of a cell affect the current drawn from it?
14. A cell of e.m.f 3.0 V is connected to a resistor of 2400Ω and when a voltmeter of very high resistance is connected across its terminals the voltmeter reads 2.5 V
(a) Explain the difference between these two voltages
(b) Calculate the internal resistance of the cell
(c) Calculate the new reading of the voltmeter if the voltmeter has a resistance of 1000Ω
15. A cell of e.m.f 12.0 V is connected to a resistor of 5000 Ω and when a voltmeter of very high resistance is connected across its terminals the voltmeter reads 10.5 V
(a) Explain the difference between these two voltages
(b) Calculate the internal resistance of the cell
(c) Calculate the new reading of the voltmeter if the voltmeter has a resistance of 2000Ω
16. The two graphs below show a specimen of metal wire at two different temperatures.
Material | βx10-4K-1 | Material | βx10-4K-1 | |
Copper | 43 | Aluminium | 38 | |
Lead | 43 | Nichrome | 1.7 | |
Eureka | 0.2 | Manganin | 0.2 | |
Iron | 62 | Platinum | 38 | |
Carbon | -0.5 | Tungsten | 60 |