Question

A coil of mean area 500 cm2 and having 1000 turns is held perpendicular to a uniform field of 0.4 gauss. The coil is turned through 180° in $\frac{1}{10}$ second. The average include emf is

• A. 0.02 V
• B. 0.04 V
• C. 1.4 V
• D. 0.08 V

Answer 1

Answer: (B)

0.04 V

Answer 2

Here, $A = 500cm^{2} = 500 \times 10^{- 4}m^{2}$

$N = 1000,B = 0.4G = 0.4 \times 10^{- 4}T$

$t = \frac{1}{10}s$

When the coil is held perpendicular to the field the normal to the plane of the coil makes an angel of $0{^\circ}$ with the field B.

$\therefore$ initial flux, $\varphi_{1} = BA\cos 0º = BA$

Final flux $\varphi_{2} = BA\cos 0º = - BA$

Average induced emf,

$\varepsilon = - N\left( \frac{\varphi_{2} - \varphi_{1}}{t} \right) = - N\left( \frac{- BA - BA}{t} \right)$

$= \frac{2NBA}{t} = \frac{2 \times 1000 \times 0.4 \times 10^{- 4} \times 500 \times 10^{- 4}}{1/10}$

$0.04V$