Page 15 - Electrostatics 11

Grade 11 © GC Shiba
Electric intensity at any point on the axis of dipole:

Dipole: Two equal and opposite charge at a distance is called a dipole.

Dipole moment (p): It is the product of one or two equal charges at dipole and
distance between them. i.e., p = q x 2l.

A O B r P

+q -q
L L

Let us consider a dipole of dipole moment P. Here +q and -q charges are at a
distance 2L and O is the Centre of dipole. Let OP = r and from figure, AP = (r +

L) and BP = (r – L)

Electric intensity at point P due to charge at point A is

⃗⃗⃗⃗⃗⃗
=

4 ( + ) 2
0
Electric intensity at point P due to charge at point B is

⃗⃗⃗⃗⃗⃗
= 4 ( − ) 2

0
Electric intensity at point P due to dipole is = −

= ( 1 − 1 )
4 0 ( − ) 2 ( + ) 2

2
( + ) − ( − ) 2
= ( )
2
4 0 ( − ) ( + ) 2
4
= ( )
2
2 2
4 0 ( − )
2( × 2 )
=
2
2 2
4 ( − )
0
2
∴ = (∵ = × 2 )
2
2 2
4 ( − )
0
This is the required expression for intensity at point P due to dipole.

15 Electrostatics