Solution
= Solution
At a perfect conductor, the reflected <electric field> cancels the incident tangential field, while their <magnetic fields> add. Thus $E_y(0)=0$ and $H_z(0)$ has peak amplitude $2A/Z_v$. Taking the zero-penetration limit, including its surface <force>, gives
$$
\boxed{P_{\rm refl}=\epsilon_0A^2=\frac{2\overline S_{\rm inc}}c.}
$$
Reversal of the normal momentum doubles the <pressure> compared with absorption at the same incident Poynting flux.