# A coil of area 500 cm2 having 1000 turns is placed such that the plane of the coil is perpendicular to a magnetic field of magnitude 4 × 10-5 weber/m2. If it is rotated by 180° about an axis passing through one of its diameter in 0.1 sec, find the average induced emf. Option 1) zero Option 2) 30 mV Option 3)   40 mV Option 4)  20 mV

Rate of change of magnetic Flux -

$\varepsilon = \frac{-d\phi }{dt}$

- wherein

$d\phi\rightarrow \phi _{2}-\phi _{1}$

$\phi _{2}-\phi _{1}-$ change in flux

Average induced EMF = $|\frac{\Delta \phi }{\Delta t}|$

$\phi_2 =-\phi_1$ (since it is turned by $180^{\circ}$

$E_{av}=\frac{|\phi _2- \phi _1}{\Delta t}=\frac{2 \phi_1}{\Delta t} =\frac{2\times NBA}{\Delta t}$

$=\frac{2\times 1000\times 4\times 10^{-5}\times 5\times 10^{-2}}{0.1} =40mV$

Option 1)

zero

Incorrect

Option 2)

30 mV

Incorrect

Option 3)

40 mV

Correct

Option 4)

20 mV

Incorrect

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