Q.

A 800 turn coil of effective area 0.05 m2 is kept perpendicular to a magnetic field 5×10-5T. When the plane of the coil is rotated by 90° around any of its coplanar axis in 0.1 s, the emf induced in the coil will be            [2019]

1 0.02 V  
2 2 V  
3 0.2 V  
4 2×10-3V  

Ans.

(1)

Here N=800, A=0.05 m2, Δt=0.1 s

B=5×10-5T

Induced emf, ε=-ΔϕΔt=-(ϕf-ϕi)Δt

ϕi=N(B·A)=800×5×10-5×0.05×cos0°=2×10-3Tm2

ϕf=0     ε=-(0-2×10-3)0.1=2×10-2V=0.02 V