Question

A pair of coils of turns $n_1$ & $n_2$ are kept close to each other. If a current passing through the first is reduced at the rate ‘r’, an emf of 2mV is developed across the other coil. If the second coil carries current which is the reduced at the rate 3r, the emf produced across the first coil will be

• A.
• B.
• C. 6mV
• D. 1.5 mV

Answer 1

The correct option is C

6mV

$e=\frac{-mdI}{dt}$

$\frac{e_1}{e_2}=\frac{(dI/dt{)}_1}{(dI/dt{)}_2}\Rightarrow =\frac{2}{e_2}=\frac{r}{3r}\Rightarrow e_2=6mV$