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1.

Magnetic Dipole and Magnetic Dipole Moment:

Magnetic length =

5

6

× Geometric length

= m ´ 2l

Units in SI System:

Quantity

Unit

Pole-strength

Ampere-metre (A-m)

Magnetic dipole moment

Ampere-metre^{2} (A-m^{2})

2.

Magnetic Induction () at Any Point Due to Short Magnetic Dipole:

Consider a magnetic dipole of dipole moment (). Consider a point P at a distance 'r' from the centre of the dipole making an angle q with the dipole axis as shown in the figure.

Derivation of Magnetic Induction ()

B=

m_{0}

4p

M

r^{3}

tanf = tanq

Special Cases:

(i)

If P is an axial point, substitute q = 0° or q = 180° in the equation

\ B_{axis} =

2M

for an axial point.

(ii)

If P is an equatorial point, substitute q = 90° in the equation

\ B_{equator} =

for an equatorial point.

Remember: Magnetic induction is a vector quantity.