2013/03/10


Making electricity flow 

1. If the bulb in a closed circuit didn’t light up, which circuit component would you check? Explain.
    l   Check the battery. If the battery was flat, the bulb will not light up.
    l   Check the bulb. If the bulb was broken, it will not light up.
    l   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) Volume control of a hi-fi set
(2) Control units of a joystick





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

5. An electrical insulators 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

7.  Switches are used to open or close a circuit.

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.

Voltage

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.

Resistance

21. The particles that make up a conductor can resist the folw of free electrons.
      This is called resistance.

22. The unit of resistance is ohm (W).

23. Resistance can be measured by a multimeter.

24. Resistance is measured in ohms.

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

26. Wires made of different materials have different resistances.

27. The resistance of a wire depends on its thickness.
      A thicker wire has a smaller resistance.

28. The resistance of a wire depends on its length.
      A long wire has a larger resistance.

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

30. List TWO examples of application of rheostats in daily lives:
(1) Volume control of a hi-fi set
(2) Control units of a joystick
Circuit symbols and circuit diagram

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

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


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