Chapter 6 – Using Electricity

1. Define electric current.
2. Explain why metals are able to conduct electricity.
3. What energy conversion takes place when electric current passes through a light bulb?
4. Any device in a circuit that converts electrical energy to another form of energy is called the  ______________________.  It could be a motor, resistor, light bulb etc.
5. Draw the symbol for the following in an electric circuit:

6. Write a list of materials needed to make the following circuit.
7. Redraw the following circuit including switches to control (a) bulb 4 only’ (b) bulb 5 and 6 only  (c) all of the bulbs.
8. Study the diagram above. 

9. Redraw the following circuit showing (a) the direction of flow of electrons.  (b)The position of an ammeter to measure the current in the circuit.  (c) The position of a voltmeter to measure the energy loss across the bulb.
10. Draw a circuit that contains

(a)   3 bulbs in series with a switch and a battery. 

(b)   A bulb in series with a power pack and a resistor and a switch and also connected to a parallel combination of 2 bulbs. 

Insert an ammeter to measure the total current in the circuit and a voltmeter to measure the energy loss across the resistor.

9. Define voltage and resistance.
10. What happens to the resistance in a wire if it is (a) very long  (b) very thick  (c) very hot?
11. If you want to minimize resistance in the wires in your circuit, what type of wires would you choose?
12. Complete the following table.

15. State Ohm’s Law.

15. (a) Calculate the voltage across a 5 Ohm light globe when the current flowing is 2 Amps.

    (b)   Calculate the voltage of a circuit when the total resistance is 6 Ohms and the current flowing in the circuit is 0.5 Amps.

    (c)   Calculate the Current flowing in a circuit if the voltage is 12 Volts and the total resistance of the circuit is 10 Ohms.

    (d)   Calculate the current flowing through a 5 Ohm resistor if the voltage drop across the resistor is 2.5 Volts.

    (e)   Calculate the resistance of a circuit if the voltage is 8 Volts and the current flowing is 1.6 Amps.

    (f)     Calculate the resistance of a light globe if there is a 4 Volt drop in electrical energy across its ends and the current flowing through it is 0.5 Amps

16. Calculate the total resistance if 5 Ohm, 4 Ohm and 10 Ohm resistors are connected in series.
17. Calculate the resistance if a 5 Ohm, 10 Ohm and another 5 Ohm resistor are connected in parallel.
18. Calculate the resistance if a 4 Ohm, 12 Ohm, 6 Ohm and a 2 Ohm resistor are connected in parallel.
19. When resistors are connected in parallel the total resistance is always less than the _____________________________________.
20. Suppose you connect an ammeter and a voltmeter into a circuit.  What might be the problem with your connections if neither of their needles moves when you switch on the power?
21. Electricity comes into your home as a 2-core cable.  What are the two insulated wires in the cable?  What is the difference between them.
22. From your switchboard, wires make up the power and the lighting circuits as well as a circuit for hot water and for the oven.  The Power wiring circuit cable is three-core.  What are the three wires?
23. Complete the table below.

1. What type of current supplies electricity to your home?  AC or DC?
2. Briefly explain the function of fuses and circuit breakers.
3. Why do some appliances not need an earth pin?
4. What problem could arise in a home, if all the copper piping was replaced by plastic pipes?
5. State the formula for electrical energy in terms of power and time.
6. Complete the following table

9. What is meant by the efficiency of an appliance?

10. A 60 Watt light bulb is 10 per cent efficient at producing light energy?

11. How do power authorities measure electrical energy usage?  What units are used?

12. If a refrigerator with a power rating of 500 Watts runs for 24 hours, what energy (in kilowatt hours) is used?

13. For how long can a 1500 watt steam-and-dry iron run if it uses 5 kilowatt hours of electrical energy.

14.How many Megajoules of electrical energy is used if a 2000 Watt electric kettle is turned on for 3 minutes?

15.Briefly explain the function of steam, running water or wind in the operation of a power station.

16.Compare and contrast the use of coal, nuclear and hydro- in power generation.

17.What is the function of a transformer and a rectifier?  How are they different?

18.Does a PC that operates on 12 V DC need a transformer-rectifier?  Explain.

19.What does the power grid mean?

Revision Points

Electrostatics Test