Question

For which of the following condition, potential energy of a dipole in an external magnetic field is zero?

• A. When $M$ and $B$ are perpendicular to each other.
• B. When $M$ and $B$ are parallel to each other.
• C. When $M$ and $B$ are ${45}^{\circ }$ to each other.
• D. Both $\left(B\right)$ and $\left(C\right)$

Answer 1

The correct option is A When $M$ and $B$ are perpendicular to each other.

Potential energy of the magnetic dipole is given as,

$U=-MB\cos \theta$

Potential energy will be zero when the $\cos \theta$ becomes zero.

So, $\theta$ should be ${90}^{\circ }$.

It means $M$ and $B$ should be perpendicular to each-other.