Question

A current I=1.5 A is flowing through a long solenoid of diameter 3.2 cm having 220 turns per cm. At its centre , a 130 turn closely packed coil of diameter 2.1 cm is placed such that the coil is coaxial with the long solenoid. The current in the solenoid is reduced to zero at a steady rate in 25 ms. What is the magnitude of emf induced in the coil while the current in the solenoid is changing?

Answer 1

Field through inner solenoid

$n=22000turns/m,i=1.5A$

$B={\mu }_{0}ni=4\pi \times {10}^{-7}\times 22000\times 1.5$

$=0.0415T$

emf induced ${ϵ}_0=\frac{d{Q}_B}{dt}$

$=\frac{130\times 0.0415\times \pi \times (0.0105{)}^2}{25\times {10}^{-3}}$

$=0.0748v$