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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.

 

 

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Mutual inductance is the induction of emf in a coil due to change in current in the neighbouring coil

\varepsilon =\frac{-d}{dt}(N\phi )=\frac{-MdI}{dt}

M is the coefficient of mutual induction or mutual inductance.

Let us consider two long coaxial solenoids of length 'l'

Let for solenoid S_{1}, the radius be r_{1} and for S_{2} radius be r_{2}, such that r_{1}< r_{2}

Due to the current flowing through S_{2} a magnetic flux \phi _{1} is set up in the coil S_{1}

Total flux linked with S_{1} is

N_{1}\phi _{1}=M_{12}I_{2} .............(1)

B_{2}= \mu_{o}n_{2}I_{2} is the magnetic field due to current I_{2} in S_{2}

The resulting flux linkage with the coil S_{1} is

N_{1}\phi _{1}=n_{1}l(\pi r{_{1}}^{2})\mu_{o}n_{2}I_{2}=\mu_{o}n_{1}n_{2}\pi r{_{1}}^{2}lI_{2}

Where

M_{12}=\mu_{o}n_{1}n_{2}\pi r{_{1}}^{2}l

Posted by

Safeer PP

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