Question

A rectangular copper coil is placed in uniform magnetic field of induction $40mT$ with its plane perpendicular to the field. The area of the coil is shrinking at a constant rate of $0.5m^2{s}^{-1}$.The emf induced in the coil is :

• A. $10mV$
• B. $20mV$
• C. $80mV$
• D. $40mV$

Answer 1

The correct option is B $20mV$

Induced EMF in a coil with varying flux through it is :

$Emf=-\frac{d\varphi }{dt}$

$=-\frac{d\left(BA\right)}{dt}$

$=-B\frac{dA}{dt}$

$⟹Emf=-40mT\times 0.5m^2{s}^{-1}=20mV$