Question

A circular coil of radius 4 cm has 50 turns. In this coil a current of 2 A is flowing. It is placed in a magnetic field of 0.1 weber/m². The amount of work done in rotating it through 180^o from its equilibrium position will be

• A. 0.1 J
• B. 0.2 J
• C. 0.4
• D. 0.8 J

Answer 1

Answer: (A)

0.1 J

Answer 2

Suppose in equilibrium wire PQ lies at a distance r above the wire AB

Hence in equilibrium $\Rightarrow m g = \frac { \mu _ { 0 } } { 4 \pi } \left( \frac { 2 i } { r } \right) \times i l$

$10 ^ { - 3 } \times 10 = 10 ^ { - 7 } \times \frac { 2 \times ( 50 ) ^ { 2 } } { r } = 0.5$ ⇒