Question

The potential energy of a bar magnet of magnetic moment 8 ${Am}^2$ placed in a uniform magnetic field of 21 cm an angle of ${120}^{\circ }$ is equal to

• A. $-16J$
• B. $16J$
• C. $-8J$
• D. $8J$

Answer 1

The correct option is D $8J$

Given: Magnetic moment = $8A{m}^2$

Magnetic field = 2T

$\theta ={120}^{\circ }$

Solution: The potential energy of a bar magnet is given by,

$U=-MB\cos \theta$

$U=-8\times 2\times \cos {120}^{\circ }$

As, $\cos {120}^{\circ }=-\frac{1}{2}$

On solving we get,

$U=+8J$

Hence, the correct option is (D).