Page 35 - Physics_Form_2

Static electricity

Factors affecting capacitance of the medium between plates Y and Z
The capacitance of a parallel plate capacitor (Figure 1.39).
is affected by three major factors, namely:
(a) area of the plates;
(b) insulating property of the medium; Y Z
and
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(c) distance between the plates.

(a) Area of the plates d
An increase in the area of the plates causes
a decrease in the potential difference
between the plates, hence an increase in
capacitance. Figure 1.39: Insulating property of materials

Plate 1 Plate 2
Z (c) Distance between plates
Y A charged capacitor is connected such
Area (A) that one plate is earthed while the other
d
is connected to an electroscope, as shown
in Figure 1.40. The distance between the
plates varies, and its effect on the leaf
divergence is noted. It is observed that
Figure 1.38: Area of plates of a capacitor the closer the plates are to each other,
the smaller the divergence and the lower
From experiments, C  A, where C is the the potential. In conclusion, capacitance
capacitance, and A is the effective area increases with the closeness of the plates.
between the plates Y and Z, as shown 1
in Figure 1.38. A distance, d, separates Thus, C  , where C is the capacitance,
the plates. If d is kept constant, and Z is d
moved parallel to Y, the overlapping area and d is the distance between plates.
is varied.
Capacitor
Brass cap
(b) Insulating property of the medium
If the air between the plates of a capacitor is
replaced with another insulating medium,
such as glass, paper, or polythene, while
the area A and the distance d remain Electroscope
constant, the capacitance increases. From
experiments, capacitance C is directly Figure 1.40: Capacitor connected to an
proportional to the insulating property electroscope

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Physics Form 2 Final.indd 29 25/10/2025 10:25