Page 104 - Physics Form 5 KSSM_Neat

Discussion:
1. Why is the E.H.T. power supply used in this activity?
2. What happens to the parallel plate electrodes when the E.H.T. power supply is switched on?
3. Why does the sprinkled semolina powder form a certain pattern when the E.H.T. power supply
is switched on?
4. What is the function of olive oil in this activity?
KEMENTERIAN PENDIDIKAN MALAYSIA
5. Name other materials beside semolina powder that can be used in this activity.
Based on Activity 3.1, when the E.H.T. power supply is switched on, the two electrodes will
be at different potentials. An electric field exists between the two electrodes. An electric field is
the region around a charged particle where any electric charge in the region will experience an
electric force. When semolina powder is placed in the electric field, it experiences an electric force.
The pattern formed by the semolina powder shows the pattern of the electric field.

Info GALLERY
+ –
An electric field line begins on
a positive charge and ends on
a negative charge. Electric field
lines also do not cross each other.
(a) A particle with (b) A particle with
positive charge negative charge

Figure 3.2 Pattern of an electric field around a positively charged
and a negatively charged particle

The electric field lines around a positive charge always point outward while the electric field
lines around a negative charge always point inward (Figure 3.2). Unlike charges attract each other
while like charges repel each other.

– + –
– + –
+ – – – + – + –
– + –
– + –

(a) Two particles with (b) Two particles with (c) A particle and a (d) Two parallel plates
unlike charges like charges plate with unlike with unlike charges
charges

Figure 3.3 Electric field patterns

Electric field patterns can be drawn using lines with arrows as shown in Figure 3.3. Every line
represents an electric field line.

94 LS 3.1.1