If $$\vec{E}$$ and $$\vec{K}$$ represent electric field and propagation vectors of the EM waves in vacuum, then magnetic field vector is given by: ($$\omega$$ - angular frequency)

For an electromagnetic wave in vacuum,

$$\vec E$$ = electric field vector

$$\vec K$$ = propagation vector

$$\vec B$$ = magnetic field vector

The magnetic field is perpendicular to both $$\vec E$$ and $$\vec K$$.

Direction of magnetic field:

$$\hat B \parallel (\hat K \times \hat E)$$

Magnitude relation:

$$B=\frac{E}{c}$$

Since,

$$c=\frac{\omega}{K}$$

therefore,

$$B=\frac{K}{\omega}E$$

Hence vector form is

$$\boxed{\vec B=\frac{1}{\omega}(\vec K\times \vec E)}$$