A linearly polarized electromagnetic wave given as $E=E_0 \hat i \cos (kz-wt)$ is incident normally on a perfectly reflecting infinite wall at $z=a$ Assuming that the material of the wall is optically inactive , the reflected wave will be given as

Question

$\begin{array}{1 1} \overrightarrow{E_r} = -E_0 \hat i \cos(kz -wt) \\ \overrightarrow{E_r} = -E_0 \hat i \cos(kz +wt) \\ \overrightarrow{E_r} = -E_0 \hat i \cos(kz +wt) \\ \overrightarrow{E_r} = E_0 \hat i \sin(kz -wt) \end{array} $