Thank you for reporting, we will resolve it shortly
Q.
In a plane electromagnetic wave, the electric field of amplitude $1\, V
\, m^{-1}$ varies with time in free space. The average energy density of magnetic field is (in $Jm^{-3}$)
We know that,
The energy density (energy per unit volume) in an electric field $E$ in vacuum
$=\frac{1}{2} \varepsilon_{0} E^{2} $
$U =\frac{1}{2} \varepsilon_{0} E^{2} $
where $ \varepsilon_{0} =8.86 \times 10^{-12} C ^{2} / N - m ^{2} $
$E =1 \,V / m $
$=\frac{1}{2} \times 8.86 \times 10^{-12} \times(1)^{2} $
$=4.43 \times 10^{-12}$
So, the average energy density of magnetic field
$=\frac{4.43 \times 10^{-12}}{2}$
$=2.21 \times 10^{-12} \,J / m ^{2}$