Even though an electric field $E$ exerts a force $qE$ on a charged particle, the electric field of an $EM$ wave does not contribute to the radiation pressure (but transfers energy). Explain.

(N/A) The electric field of an electromagnetic wave is an oscillating field, and so is the electric force it exerts on a charged particle. The force is given by $F = qE_0 \sin(\omega t - kx)$. When averaged over an integral number of cycles, the net force is zero because the direction of the force reverses every half cycle. Since radiation pressure is defined as the time-averaged force per unit area, the oscillating electric field does not contribute to it. However, the electric field does perform work on the charge, thereby transferring energy.