Page 4 - PRE-U STPM PHYSICS TERM 2

Physics Term 2 STPM Chapter 13 Capacitors

INTRODUCTION

1. Capacitors are widely used in electronic circuits. Capacitors store electric charge.
2. Electrons flow in and out but not through a capacitor. A capacitor blocks direct current but

alternating current is able to pass through it.

13 3. Basically, a capacitor consists of two parallel metal plates with an insulator known as dielectric 13
in between.
4. Example of dielectrics are air, paper, wax and mica.

Figure 13.1

Figure 13.2

5. Figure 13.1 shows the circuit symbol of a capacitor.
6. Figure 13.2 shows capacitors of various sizes used in electrical and electronic circuits.

13.1 CapacitanceCapacitance
13.1
Learning Outcome 2016/P2/Q3, 2018/P2/Q4

Students should be able to:
• defi ne capacitance

1. Figure 13.3 shows what happens when a capacitor is
connected to a battery. Electrons from the battery charges
the plate X of the capacitor with a charge of –Q and a
charge of +Q is induced on the opposite plate Y. Hence, _ X
the charge on both plates of the capacitor is the same Battery _ + _ _ _ Capacitor
+ +
+
magnitude but opposite in sign. + Y
2. As the charges on the plates of the capacitor increase, the Figure 13.3
potential difference across the capacitor increases until it
is equal to the e.m.f. of the battery.
3. The charges remain in the capacitor even after the battery is disconnected.

4. The quantity of charge a capacitor is able to store depends on its capacitance.
5. The capacitance C of a capacitor is the ratio of the charge on a plate of the capacitor to
the potential difference between the plates.
Charge on either plate of capacitor –Q +Q
Capacitance, C = —————————————————–
Potential difference between the plates
V
Q
C = — Figure 13.4
V
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13 Physic T2.indd 44 10/18/18 3:18 PM