A long solenoid ‘S’ has ‘n’ turns per meter,


A long solenoid ‘S’ has ‘n’ turns per meter, with diameter ‘a’. At the centre of this coil, we place a smaller coil of ‘N’ turns and diameter ‘b’ (where b < a). If the

current in the solenoid increases linearly, with time, what is the induced emf appearing in the smaller coil. Plot graph showing nature of variation in emf, if

current varies as a function of mt2 + C.


The varying magnetic field in the solenoid is given as:

B1(t) = μonI(t)

Magnetic flux in the second coil is

Φ2 = μonI(t).πb2

Therefore, the induced emf in the second coil due to solenoid’s varying magnetic field is –μoNn πb22mt

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