Download the app



A long coaxial cable consists of two thin-walled conducting cylinders with inner radius 2 cm and outer radius 8 cm. The inner cylinder carries a steady current 0.1 A, and the outer cylinder provides the return path for that current. The current produces a magnetic field between the two cylinders. Find the energy stored in the magnetic field for length 5 m of the cable. Express answer in nano-J (use ln2 = 0.7).


The magnetic field inside is only due to the current of the inner cylinder.


Magnetic field energy density is not uniform in the space between the cylinders. At a distance r from the centre,


Energy in volume of element (length l)

dUB=uBdV=μ0i28π2r22πldr=μ0i2l4πdrr UB=μ0i2l4πabdrr=μ0i2l4πlnba

Using values, we get U = 7 nJ

Talk to our academic expert!


Are you a Sri Chaitanya student?

Similar Questions

A capacitor of capacity 2μF is charged to a potential difference of 12 V.It is then connected across an inductor of inductance 6μH. What is the current (in A) in the circuit at a time when the potential difference across the capacitor is 6.0 V?

phone icon
whats app icon