A bar magnet of magnetic moment 3 J/T lies aligned with the directions of a uniform magnetic field of 0.2 T. The amount of work, required so as to align its magnetic moment opposite to the field direction is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 1.2 J
The work required rotate a magnetic moment $\vec M$ in a magnetic field $(\vec B)$ is -
$W=-MB(\cos θ_2-\cos θ_1)$
$M=3J/T$
$B=0.2T$
$θ_1=0°,θ_2=180°$
$W=-(3)(0.2)(\cos 180-\cos 0)$
$=1.2J$