Page 106 - Physics Form 5 KSSM_Neat

Behaviour of Charged Particles in an Electric Field
In an electric field, there is electric charge which can be positive or negative. Like charges repel
each other while unlike charges attract each other. What will happen to charged particles when
they are placed in an electric field?

Activity 3.2 Teacher’s demonstration

Aim: To show the effects of an electric field on a charged object
Apparatus: Extra high tension (E.H.T.) power supply, metal plates and retort stands
Materials: Polystyrene ball wrapped in aluminium foil, nylon string and candle
Instructions:
1. Set up the apparatus as shown in Figure 3.6.

Nylon Polystyrene ball
string wrapped in Retort stands
aluminium foil Metal plates

E.H.T. E.H.T.
power supply power supply
Metal Metal
plate plate
AC + DC – Candle AC + DC –

Retort stands
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Figure 3.6 Figure 3.7
2. Switch on the E.H.T. power supply. Displace the polystyrene ball so that it touches one of the
metal plates and release the ball. Record your observation.
3. Repeat step 2 by:
(a) decreasing the distance between the two metal plates.
(b) increasing the voltage of E.H.T. power supply.
4. Switch off the power supply and replace the polystyrene ball with a lighted candle as shown in
Figure 3.7.
5. Switch on the E.H.T. power supply. Observe the effects on the candle flame. Record your
observations.
6. Switch off the E.H.T. power supply. Reverse the connection at the power supply terminals and
then switch on again. Observe the effects on the candle flame. Record your observations.
Discussion:
1. Why must the polystyrene ball be wrapped in aluminum foil?
2. What is the function of the nylon string?
3. What will happen to the movement of the polystyrene ball if the distance between the metal
plates increases?

96 LS 3.1.3