Page 78 - Physics 10_Float

ELECTROSTATICS

+Q
insulator. This medium is known as dielectric. Q

Potential and Potential
Energy
Electric potential is a
(a) A B (b) A B
( . ) characteristic of the field of
K + – s o u r c e c h a r g e a n d i s
V
independent of a test charge
that may be placed in the field.
Fig. 13.13 (a) Parallel plate capacitor (b) Plates of capacitor connected But, potential energy is a
with battery characteristic of both the field
If a capacitor is connected to a battery of V volts, then the and test charge. It is produced
battery transfers a charge +Q from plate B to plate A, so that due to the interaction of the
-Q charge appears on plate A and +Q charge appears on plate field and the test charge
B . placed in the field.
The charges on each plate attract each other and thus
remained bound within the plates. In this way, charge is
stored in a capacitor for a long time.
Also, the charge Q stored on plates is directly proportional to
the potential difference V across the plates i.e.,
F 
q
q
1 ﻮ
Q V
Q = CV ........(13.8)
where C is the constant of proportionality, called the
capacitance of the capacitor and is defined as the ability of
the capacitor to store charge. It is given by the ratio of charge
and the electric potential as:
Q
C =
V

SI unit of capacitance is farad (F), defined as:

If one coulomb of charge given to the plates of a capacitor
produces a potential difference of one volt between the plates
of the capacitor then its capacitance would be one farad.

farad is a large unit, usually, we use a smaller unit such as
micro farad (µF), nano farad (nF) and pico farad (pF) etc.

Example 13.2: The capacitance of a parallel plate capacitor is
100 F. If the potential difference between its plates is µ
78 Not For Sale – PESRP