The magnetic flux linked with a coil at any instant 't' is given by `phi = 5t^3 - 100 t+300`, the e.m.f. induced in the coil at t = 2 second is

Options

A. 40 V
B. `-40 "V"`
C. 300 V
D. 140 V

Answer

A

Explanation

The induced emf `e=-(d phi)/(dt)`
So, `" "e=-(d)/(dt)(5t^(3)-100t+300)`
or `" "e=-(15t^(2)-100)`
Induced emf at t = 2 s
`e=-(15xx4-100)=+40`