In the inductive circuit given in the figure, the current rises after the switch is closed. At instant when the current is 15 mA, then potential difference across the inductor will be-

Options

A. Zero
B. 240V
C. 180V
D. 60V

Answer

C

Explanation

At any instant
`240 = iR + L (di)/(dt)`
`rArr 240 = 15 xx 10^(-3) xx 4000 + L (di)/(dt)`
`rArr L (di)/(dt) = 240 - 60 = 180 V `