Question

The current in a coil changes from $1mA$ to $5mA$ in $4$ milli second. If the coefficient of self-induction of the coil is $10mH$ the magnitude of the "self-induced" emf is:

• A. $10mV$
• B. $5mV$
• C. $2.5mV$
• D. $1mV$

Answer 1

Answer: (A)

$10mV$

Self induced emf, $e=-L\frac{dI}{dt}$

$=10\times {10}^{-3}\times \frac{4\times {10}^{-3}}{4\times {10}^{-3}}=10mV$