Consider a small cube of volume `1 mm ^3` at the centre of a circular loop of radius 10 cm carrying a current of 4 A. Find the magnetic energy stored inside the cube.

Explanation

magnetic field at centre
`B=(mu_(0)i)/(2r)`
Energy density `u=(B^(2))/(2mu_(0))`
Energy stored in the cube
`U=uV_(0)=(B^(2))/(2mu_(0))V_(0)` , `V_(0)` : volume of the cube
`=(1)/(2mu_(0))xx((mu_(0)i)/(2r))^(2)V_(0)`
`=(mu_(0)i^(2)V_(0))/(8r^(2))`
`=(4pixx10^(-7)xx4^(2)xx1xx10^(-9))/(8xx(0.1)^(2))`
`=8pixx10^(-14)J`