[4 31(a)] is very similar to an expression obtained
earlier for the electric field of a dipole The similarity may be seen if we
substitute,
 
0
1/0
µ
ε
→
Rationalised 2023-24
129
Moving Charges and
Magnetism
e
m→
p  (electrostatic dipole)
 
B→
E   (electrostatic field)
We then obtain,
3
0
2
4
e
εx
=
π
p
E
which is precisely the field for an electric dipole at a point on its axis considered in Chapter 1, Section 1