Question

A sky wave with a frequency $55MHz$ is incident on $D-$region of earth's atmosphere at ${45}^o$. The angle of refraction is (electron density for $D-$regions is $400electron/c{m}^3$) :

• A. ${60}^o$
• B. ${45}^o$
• C. ${30}^o$
• D. ${15}^o$

Answer 1

The correct option is B ${45}^o$

$n_{eff}=n_0\sqrt{1-\left(\frac{80.5N}{v^2}\right)}=1\sqrt{1-\frac{80.5\times (400\times {10}^6)}{(55\times {10}^6{)}^2}}\approx 1$
Also : $n_{eff}=\frac{\sin i}{\sin r}\Rightarrow \sin r=\sin i\Rightarrow r=i={45}^o$