Unit8 Making Use of Electricity

Worksheet 8.1 --- Pre-Study

23.1 Making electricity flow

1. If the bulb in a closed circuit didn’t light up, which circuit component would you

check? Explain.

Check the battery. If the battery was flat, the bulb will not light up.

Check the bulb. If the bulb was broken, it will not light up.

Check the contacts. If the contact were loose, the bulb will not light up.

2. A continuous and complete circuit is called a closed circuit,

while a circuit with a gap is called an open circuit.

3. Write down the TWO conditions needed for electric current to flow.

(1) The circuit is complete

(2) There is a source of electricity

4. An electrical conductor allows an electric current to pass through.

5. An electrical insulator does not allow electric current to flow through.

6. Determine whether the following materials are conductors or insulators.

Materials Conductor or

insulator? Materials

Conductor or

insulator?

Wooden

chopsticks Insulator Aluminium foil conductor

Iron paper clip Conductor Rubber tubing insulator

Glass rod Insulator Coins conductor

Steel spoon Conductor Salt water conductor

Wet wood Conductor Oil insulator

Cola Conductor Graphite conductor

Tap water Conductor Distilled water insulator

Air Insulator Copper conductor

Paper Insulator Sellotape insulator

23.2 Electric current

8. An atom consists of a positively charged nucleus surrounded by

many tiny negatively charged particles called electrons.

9. The flow of free electrons is called an electric current.

10. We can use an ammeter to measure the size of an electric current.

11. The unit of electric current is ampere (A).

Small currents are measured in milliamperes (mA).

12. 1 mA = 0.001 A

13. Electric current can be measured by an ammeter.

14. Electric current is measured in amperes.

23.3Voltage

15. Voltage is the ‘electrical push’ that makes electrons flow in a circuit.

16. We can use a voltmeter to measure voltage.

17. The unit of voltage is volt (V).

18. Voltage can be measured by a voltmeter.

19. Voltage is measured in volts.

20. Voltage can cancel each other if the cells are connected in opposite direction.

23.4Resistance

21. The particles that make up a conductor can resist the flow of free electrons.

This is called resistance.

22. The unit of resistance is ohm ().

23. Resistance can be measured by multimeter.

24. Resistors are used to limit or control the size of the current in a circuit.

25. Wires made of different materials have different resistances.

26. The resistance of a wire depends on its thickness.

A thicker wire has a smaller resistance.

27. The resistance of a wire depends on its length.

A long wire has a larger resistance.

28. Unlike a resistor that has a fixed resistance, the resistance of a rheostat can be

changed.

29. List TWO examples of application of rheostats in daily lives:

(1) Volume control of a hi-fi set

(2) Control units of a joystick

24.1 Circuit symbols and circuit diagram

30. We can draw a circuit diagram to represent an actual circuit.

31. Draw the circuit symbol of the following circuit components.

Circuit component Circuit symbol Circuit component Circuit symbol

Connecting wire

Battery

Swtich

Light bulb

Ammeter

Voltmeter

Resistor

Rheostat

24.2 Series circuits and Parallel Circuits

32.

Electric Circuit Features

Series circuit ** There is only one path for electric current to flow.

** Currents at different points in the circuit are the same in size.

Parallel circuit ** There is more than one path for electric current to flow.

** Currents at different points in the circuit may be different is size.

33. Series circuit:

When light bulb are connected inseries,

there is only one path for the electric current to flow.

Therefore, if one of the bulbs burns out or is removed,

the circuit will become incomplete and other bulb will go out.

34. Parallel circuit:

When light bulbs are connected inparallel,

there are several branches through which the electric current can flow.

Therefore, if one of the bulbs burns out or is removed,

the electric current can still pass through other branches.

Therefore, other bulbs can still light up.

35. In a series circuit, the current is the same (the same / different) at different points

in the circuit.

36. In a parallel circuit,

(a) the current flowing in mainloop is the sum of the currents flowing in the branches.

(b) A larger current passes through the branch with a lower resistance.