A coil of circular cross - section having 1000 turns and `4cm^(2)` face area is placed with its axis parallel to a magnetic field which decreases by `10^(-2)"Wb m"^(-2)` in 0.01 s. the e.m.f induced in the coil is :

Options

A. 400 mV
B. 200 mV
C. 4 mV
D. 0.4 mV

Answer

A

Explanation

Given : No. of turns N = 1000
Face area, `A=4 cm^(2)=4xx10^(-4)m^(2)`
Change in magnetic field,
`Delta B = 10^(-2)wbm^(-2)`
Time taken, `t=0.01 s=10^(-2)` sec
Emf induced in the coil e = ?
Applying formula,
Induced emf, `e=(-d phi)/(dt)`
`=((Delta B)/(Delta t))A cos theta`
`=(1000xx10^(-2)xx4xx10^(-4))/(10^(-2))=400mV`