Question

The flux linked with a coil of any instant t is given by $\varphi =t^2-5t+25$. The induced emf at $t=4$s is?

• A. $2$V
• B. $-3$V
• C. $4$V
• D. $-4$V

Answer 1

The correct option is B $-3$V

Induced emf is given by
$e=-\frac{d\varphi }{dt}$
$=-\frac{d}{dt}(t^2-5t+25)$
$=-(2t-5)$
$=5-2t$
At $t=4s$,
$e=5-2\times 4$
$=5-8$
$=-3V$.