The electric field of a plane electromagnetic wave varies with time of amplitude 2Vm−1 propagating along z-axis. The average energy density of the magnetic field is( in Jm−3 )

Average energy density of magnetic field=(Brms)22μ0=(B0/2)22μ0=14B02μ0But B0=E0CAverage energy density of magnetic field is14E02C2μ0=14∈0E02              ∴  ∈0=1C2μ0Average energy density of magnetic field =14×8.85×10−12×22=8.85×10−12J/m3