A Pair of coils of turns `n_(1)` and `n_(2)` are kept close together. Current passing through the first is reduced at r, and emf 3 mV is developed across the other coil. If the second coil carries current which is then reduced at the rate 2 r, the emf produced across the first coil will be

Options

A. `(6n_(1))/(n_(2))mV`
B. `(6n_(2))/(n_(1))mV`
C. 6 mV
D. 3/2 mV

Answer

C

Explanation

`M_(12)=M_(21')`, when rate of change of current is doubled, induced emf also becomes two times.
Thus, emf produced across the first coil is 6 mV.