Question

The unit of pole strength is
(A) $A{m^2}$
(B) $A{m^{ - 1}}$
(C) $Am$
(D) $A{m^{ - 2}}$

Answer 1

Hint:The pole strength is the force experienced by the unit magnetic pole which is at some distance from the magnet. This is obtained by the dipole moment per unit length of the magnet. This value determines the strength of the magnet.

Useful formula:
$p = \dfrac{d}{l}$

Where $p$ is the magnetic pole strength, $d$ is the magnetic dipole moment and $l$ is the length of the magnet.

Complete step by step solution:
The pole strength is obtained by dividing the magnetic dipole moment with the length of the magnet. If the value of the pole strength is greater, then the strength of the magnet is also greater. Let us consider the formula of the magnetic pole strength,

$p = \dfrac{d}{l}$

From the formula, the unit of the magnetic dipole moment is $A{m^2}$ and the $SI$ unit of the length is $m$ . Hence the magnetic pole strength unit is calculated by dividing the unit of the magnetic dipole moment and the length of the magnet.

$p = \dfrac{{A{m^2}}}{m}$

By simplifying the above step, we get

$ = Am$ .

Hence the unit of the magnetic pole strength is obtained as $Am$ .

Thus the option (C) is correct.

Note:In the concept of the magnetic pole strength, the unit magnetic pole is considered. It does not exist in reality. The magnet is said to have the two equal and opposite poles at its ends like the North Pole and the South Pole. These two poles cannot be separated into individual. If separated again the new North and South Pole formed in the new separated magnet. But this imaginary concept is used only for the understanding of the concept of the strength of the magnet and the electric field.