Physics - EMI/AC Question with Solution | TestHub

Induced e.m.f. $(\epsilon )=\frac{Ldi}{dt}$ and current $(i)=\frac{\epsilon }{R}=\frac{1}{R}\times \frac{Ldi}{dt}$ $$\text{ or, }\frac{L}{R}=\frac{idt}{di}=\frac{\text{ current }\times \text{ time }}{\text{ current }}=\text{ time. }$$ In order to increase the rate of increase of current through a solenoid, we increase the time constant $(L/R)$. Since $L$ of the given solenoid is constant, therefore we use a high resistance in series with it.