Question

A 250-turn rectangular coil of length $2.1cm$ and width $1.25cm$ carries a current of 85 $\mu A$ and subjected to a magnetic field of strength $0.85T$. Work done in 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}$
$W=9482812.5\times {10}^{-12}$
$W=9.4\mu J$