Define mutual inductance between a pair of coils. Derive an expression for the mutual inductance of two long coaxial solenoids of same length wound one over the other.
Mutual inductance is the induction of emf in a coil due to change in current in the neighbouring coil
M is the coefficient of mutual induction or mutual inductance.
Let us consider two long coaxial solenoids of length 'l'
Let for solenoid , the radius be
and for
radius be
, such that
Due to the current flowing through a magnetic flux
is set up in the coil
Total flux linked with is
is the magnetic field due to current
in
The resulting flux linkage with the coil is
Where