Question

Calculate the self-inductance
of a coaxial cable of length 1 and carrying a
current I. The current flows down the inner
cylinder with radius a, and flows out of
the outer cylinder with radius b.​

Answer 1

Answer:

Total energy stored per unit volume =2μ0B2

Magnetic field at a distance r from the central axis of cable is given by 

B=2πrμ0I

Hence energy stored=∫2μB2dV

=∫ab2μ0B22πrldr

=4πμ0I2lln(ab)

=4πμ0×0.12×5×ln4

=7nJ

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