1. 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.
Conductor or Conductor or
Materials Materials
insulator? insulator?
Wooden
Insulator Aluminium foil conductor
chopsticks
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
2. 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 ().
3. 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
4. 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.
