Question

A rectangular coil area A, of ${}^{\prime }{n}^{\prime }$ turns carrying a current I is placed in a magnetic field B. When is the torque on the coil doubled?

• A. Both A and I are doubled.
• B. Both A and B are doubled
• C. Only A is doubled
• D. Only n is halved

Answer 1

The correct option is C Only A is doubled

Given :

Number of turns $n$

Area of rectangular coil $A$

Current $I$

Magnetic field $B$

Solution :

We know that $\tau =\overrightarrow{M}\times \overrightarrow{B}$

Hence, $\tau =MB\sin \theta$

where, $M=nIA$

So, $\tau =nIAB\sin \theta$

Som When $A$ is doubled then $\tau$ is also doubled.

Correct Opt : {C}