Suppose a cube of volume `2mm^(3)` is placed at the centre of a circular loop of radius 5 cm carrying current 2A.
Find the magnetic energy stored inside the cube.

Explanation

Magnetic field at centre of the circular loop is given by
`B=(mu_(0)i)/(2R)`
We know, energy density, `mu=(B^(2))/(2mu_(0))`
and energy stored in the cube will be given by
`U=muV_(0)=(B_(2))/(2mu_(0))V_(0)`
where, `V_(0)` is the volume of the cube.
Substituting the values in the above equation,
`=(1)/(2mu_(0))xx((mu_(0)i)/(2R))^(2)V_(0)=(mu_(0)i^(2)V_(0))/(8R^(2))`
`=(4pixx10^(-7)xx2^(2)xx2xx10^(-9))/(8xx(0.05)^(2))=16pixx10^(-14)J`