Compare the expression for magnetic energy density with electrostatic energy density stored in the space between the plates of a parallel plate capacitor.

Explanation

The electrostatic energy stored
`U= (1)/(2)(q^(2)/ (2epsilon_(0)A)) xx d" "...(i)`
( where C is the capacitance, `C = (epsilon_(0)A)/(d))` q is the charge upon capacitor)
Now the electric field in the space (between plates of capacitor)
`E= (q)/(epsilon_(0)A)" "...(ii)`
From equation (i) and (ii)
`U= (1)/(2)((q)/(epsilon_(0)A))^2 xx epsi_0 xx A xx d`
`impliesU=(1)/(2)epsilon_(0) E^(2) xx "volume"`
Hence `(U)/("Volume")=1/2 epsi_0) E^2" "(iii)`
This expression can be compared with magnetic energy per unit volume which is equal to `(B^(2))/(2mu_(0))" "(iv)`