3) and (5 6) with the corresponding equations
for electric dipole (Chapter 1), suggests that magnetic field at large
distances due to a bar magnet of magnetic moment m can be obtained
from the equation for electric field due to an electric dipole of dipole moment
p, by making the following replacements:
E→
B , p
m
→
, 
0
0
1
4
4
µ
ε
→
π
π
In particular, we can write down the equatorial field (BE) of a bar magnet
at a distance r, for r >> l, where l is the size of the magnet:
0
3
4
E
r
= −µ
π
m
B
(5 4)
Likewise, the axial field (BA) of a bar magnet for r >> l is:
0
3
2
4
A
r
=µ
π
m
B
(5 5)
Rationalised 2023-24
141
Magnetism and
Matter
Equation (5