Problem 4.199

A standing electromagnetic wave with electric component $\mathbf{E}=\mathbf{E}_{m} \cos k x \cdot \cos \omega t$ is sustained along the $x$ axis in vacuum. Find the magnetic component of the wave $\mathbf{B}(x, t) .$ Draw the approximate distribution pattern of the wave's electric and magnetic components $(\mathbf{E}$ and $\mathbf{B})$ at the moments $t=0$ and $t=T / 4,$ where $T$ is the oscillation period.