Question

The area of a circular coil of $2000$ turns is $70c{m}^2$. The coil is kept normal to the field of $0.3W/m^2$ and rotated through ${180}^{\circ }$. The emf in volts generated in $1sec$ will be :

• A. $12$
• B. $4.2$
• C. $6$
• D. $84$

Answer 1

Answer: (B)

$4.2$

$E_{av}=\frac{-\Delta \varphi }{\Delta t}$

$=\frac{{\varphi }_1-{\varphi }_2}{t_2-t_1}$

$=\frac{NBA\cos 0^o-NBA\cos {180}^o}{\Delta t}$

$=\frac{2\times 2000\times 0.3\times 0.007\times \left(0.5\right)}{1sec}$

$=4.2V$