Page 10 - Electrostatics 11

Grade 11 © GC Shiba
Electric potential: It is measured in terms of work done for which a reference

point is considered as infinity where potential is zero. (from Coulomb's law we
1
know that ∝ i.e., when → ∞, → 0).
2

Electric potential = [ ]
ℎ

or, = [ ]

Its SI unit is Volt (joule per coulomb) and CGS unit is stat volt.

1 volt = 1/300 stat volt

1 volt: Electric potential at a point in the electric field is said to be 1 V if 1 joule
work is done in a moving charge of 1 coulomb from infinity to that point.

☻ Define electric potential and derive an expression for it due to point charge.

Electrical potential at any point in the electric field is defined as the amount

of work done in taking unit positive charge (+1) from infinity to the point under
consideration.

P dr
⃗⃗

+Q
r (+1)

let us consider a point P in the electric field of +Q charge at a distance r. We

want to find electric potential at point P. Put +1 charge at point P.

The electric force acting at a point P between +Q and +1 according to Coulomb's

formula is

= Where is permittivity of the free space.
0
4 2
0
Now +1 charge is displaced by very small distance dr towards +Q charge then

⃗ ⃗⃗⃗⃗⃗
work done (dw) = .

= F dr cos180 0

= - F dr

10 Electrostatics