Physics - EM Waves Question with Solution | TestHub

Given $\overrightarrow{E}=E_0\cos (\omega t-kz)\hat{\mathrm{i}}$:

Clearly, $(\omega t-kz)$ term represents, electromagnetic wave is travelling along $+z$ direction or along $\hat{\mathrm{k}}$.

Now, in vector form, direction of electromagnetive wave is given by $\hat{C}=\hat{E}\times \hat{B}$. Therefore, magnetic field is along $\hat{\mathrm{j}}$. 

Also, we know that $B_0=\frac{E_0}{C}$, where $C$ is speed of light.

Therefore, $\overrightarrow{B}=\frac{E_0}{C}\cos (\omega t-kz)\hat{\mathrm{j}}$.$$