An electromagnetic wave of frequency 1×1014 hertz is propagating along z-axis. The amplitude of electric field is 4 V/m. If ε0=8.8×10-12C2/N-m2, then average energy density of electric field will be:

Given: Amplitude of electric field,  E0=4v/m  Absolute permitivity,  ε0=8.8×10-12c2/N-m2  Average energy density uF=?  Applying formula,   Average energy density uE=14ε0E2 ⇒  uE=14×8.8×10-12×(4)2 =35.2×10-12 J/m3