Question

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

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

Answer 1

The correct option is B ${45}^{\circ }$

$$\begin{array}{c}Accordingtoquestion...................\\ n_{effective}=n_0\sqrt{1-\left(\frac{80.5N}{v^2}\right)}\\ =1\sqrt{1-\frac{80.5\times (400\times {10}^6)}{{(55\times {10}^6)}^2}}\\ \Rightarrow n_{effective}\approx 1\\ \Rightarrow n_{effective}=\frac{\sin i}{\sin r}\\ \Rightarrow \sin r=\sin 1\\ \therefore r={45}^0\\ sothatthecorrectoptionB.\end{array}$$