Q. A small coil of $N$ turns has an effective area $A$ and carries a current $I$. It is suspended in a horizontal magnetic field $\overrightarrow{B}$ such that its plane is perpendicular to $\overrightarrow{B}$. The work done in rotating it by $180{^\circ}$ about the vertical axis is
A) $NAIB$
B) 2$NAIB$
C) $2\pi NAIB$
D) $4\pi NAIB$
Explanation
(b) $W = MB(\cos\theta_{1} - \cos\theta_{2})$
$= (NiA)B\left( \cos{0{^\circ}} - \cos{180{^\circ}} \right) = 2NAIB$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.