Discussion Forum



1)

A rectangular loop of sides 10 cm and 5 cm carrying a current I of 12A is placed in different orientations as shown in the figures below.

262202119_m34.JPG

   If there is a uniform magnetic field of 0.3 T in the positive z-direction in which orientations the loop would be in (i) stable equilibrium and (ii)  unstable equilibrium?


A) (a) and (b) respectively

B) (a) and (c) respectively

C) (b) and (d) respectively

D) (b) and (c) respectively

Answer:

Option C

Explanation:

Since B is uniform only torque acts on a current-carrying loop.

  As,    $\tau=M\times B$ 

  $\Rightarrow$          $|\tau|=|M||B|\sin\theta$

 For orientation shown in (b)  $\theta=0^{0},\tau=0$

             (stable equilibirum)

  and for (d)  $\theta=\pi,\tau=0$  (unstable equilibium)