Question

A 250- Turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 $\mu A$ and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by ${180}^0$ against the torque is:

• A. $9.4\mu J$
• B. $2.3\mu J$
• C. $1.15\mu J$
• D. $9.1\mu J$

Answer 1

The correct option is A $9.4\mu J$

Given that,

Length, $l=2.1cm$

Width, $W=1.25cm$

Current, $i=85\mu A$

Magnetic field, $B=0.85T$

Work done in rotating the coil is given by:

$W=MB(\cos {\theta }_1-\cos {\theta }_2)$

$W=MB(\cos 0-\cos 180)$

$W=2MB$

$W=2\left(NIA\right)B$

$W=2\times 250\times 85\times {10}^{-6}\times (1.25\times 2.1\times {10}^{-4})\times 85\times {10}^{-2}$

$W=9482812.5\times {10}^{-12}$

$W=9.4\mu J$