An electromagnetic wave of frequency 5GHz, is travelling in a medium whose relative electric permittivity and relative magnetic permeability both are 2. Its velocity in this medium is ______ $$\times 10^7$$ m s$$^{-1}$$.

We have an electromagnetic wave of frequency 5 GHz travelling in a medium with relative electric permittivity $$\varepsilon_r = 2$$ and relative magnetic permeability $$\mu_r = 2$$.

The velocity of an electromagnetic wave in a medium is given by $$v = \frac{c}{\sqrt{\mu_r \varepsilon_r}}$$, where $$c = 3 \times 10^8$$ m/s is the speed of light in vacuum.

Substituting the values, $$v = \frac{3 \times 10^8}{\sqrt{2 \times 2}} = \frac{3 \times 10^8}{\sqrt{4}} = \frac{3 \times 10^8}{2}$$.

$$v = 1.5 \times 10^8 = 15 \times 10^7$$ m/s.

So, the answer is $$15$$.