Question

A rectangular loop of sides 10 cm and 5 cm carrying a current I and 12 A is placed in different orientations as shown in the figures above.
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 1

The correct option is C (B) and (D), respectively

$U=-\overrightarrow{M.}\overrightarrow{B}=-MBCos\theta$
So, $U_{min}$ when $\theta =0^0\Rightarrow$ Stable equilibrium
$U_{max}$ when $\theta ={180}^0\Rightarrow$ Untable equilibrium