Question

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

Answer 1

Magnetic Pole strength can be defined as force acting per magnetic field, which is $m = \dfrac{F}{B}$. Magnetic pole strength is denoted by $m$. Thus, by putting the respective units of force and magnetic field, we can obtain the unit of magnetic field.

Complete answer:
In simple words we can define magnetic pole strength as the ability of a magnetic pole to attract magnetic materials towards itself provided it is of the opposite pole. Thus, we can define magnetic pole strength in terms of force and magnetic field.

Now let us consider a charge moving inside a magnetic field. Due to the magnetic field a force is experienced by the charge. This force lets us consider it to be denoted by $F$ and the magnetic field be denoted by $B$.
Therefore, as we discussed above Magnetic pole strength is given by $m = \dfrac{F}{B}$. The charge moving inside the magnetic field, experiences the force $F$, the expression of this force is given by $F = qvB$ ;
Where,
$F$ Is the force experienced by the charged body.
$q$ Is the charge of the body
$B$ is the magnetic field in which the body moves
$v$ is the velocity with which the charge moves.
This force is known as the Lorentz force.
Putting the expression of force in the formula for magnetic pole intensity,
We obtain:
$F = \dfrac{{qvB}}{B}$
On further solving:
$F = qv$
We know, the SI unit for velocity is $m/s$ and that of charge is C.
Therefore,
$F = Cm/s$
Rearranging the equation, we obtain:
$F = C/sm$
We know, charge per unit time is current, and SI unit of current is Ampere.
So, we write:
$F = Am$

Thus option (C) is correct.

Note: Magnetic field is defined as the effect of magnetic materials on a moving charge. It is a vector quantity which is given by the Lorentz equation. SI unit of magnetic pole strength is also weber $(Wb)$, when it is described as force per unit magnetic field intensity.