Consider a bar magnet NS of length 2l and pole strength m placed in a uniform magnetic field of induction B at an angle θ with the direction of the field (Fig.).

Due to the magnetic field B, a force mB acts on the North Pole along the direction of the field and a force mB acts on the South Pole along the direction opposite to the magnetic field. These two forces are equal and opposite, hence constitute a couple.

The torque τ due to the couple is

Vectorially

The direction of τ is perpendicular to the plane containing and .

If B = 1 and θ = 90^{0}

Then from equation (2),

Hence, the *moment of the magnet M is equal to the torque necessary to* *keep the magnet at right angles to a magnetic field of unit magnetic induction.*

## How useful was this post?

Click on a star to rate it!

Average rating 4.3 / 5. Vote count: 55

## We are sorry that this post was not useful for you!

Let us improve this post!

Thanks for your feedback!