Here, in electromagnetic wave, the electric field vector is given as, $\mathbf{E}=\left(E_1\hat{\mathbf{i}}+E_2\hat{\mathbf{j}}\right) \cos (kz-\omega t)$

In electromagnetic wave, the associated magnetic field vector,

$$\begin{gathered} \hat{\mathrm{B}}=\hat{\mathrm{c}}\times \hat{\mathrm{E}} \\ =\hat{\mathrm{k}}\times \left(\frac{{\mathrm{E}}_1\hat{\mathbf{i}}+{\mathrm{E}}_2\hat{\mathbf{j}}}{\sqrt{{{\mathrm{E}}_1}^2+{{\mathrm{E}}_2}^2}}\right) \\ =\frac{{\mathrm{E}}_1\hat{\mathbf{j}}-{\mathrm{E}}_2\hat{\mathbf{i}}}{\sqrt{{{\mathrm{E}}_1}^2+{{\mathrm{E}}_2}^2}} \end{gathered}$$

$$\begin{gathered} \mathbf{\left|}\mathbf{B}\mathbf{\right|}=\frac{\left|E\right|}{c} \\ \Rightarrow \overrightarrow{\mathbf{B}}=\left(\frac{E_1\hat{\mathbf{j}}-E_2\hat{\mathbf{i}}}{c}\right) \cos (kz-\omega t) \end{gathered}$$

E and B are perpendicular to each other and the propagation of electromagnetic wave is perpendicular to E as well as B. Here, E and B are confined in xy-plane and are mutually perpendicular and propagating in z-direction. The given electromagnetic wave is plane polarised.