A long solenoid has an area of cross-section of 
, as shown in the figure below.
A coil C consisting of 160 turns of insulated wire is wound tightly around the centre of the solenoid. The magnetic flux density 
at the centre of the solenoid is given by the expression
where 
is the current in the solenoid, 
is a constant equal to 
and 
is the permeability of free space. Calculate, for a current of 
in the solenoid,
the magnetic flux density at the centre of the solenoid,
the flux linkage in the coil C.
State Faraday’s law of electromagnetic induction.
The current in the solenoid in (a) is reversed in direction in a time of 
. Calculate the average e.m.f. induced in coil C.
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