Question

A transmitting antenna radiates 251 W isotropically. A receiving antenna, located 100 m away from the transmitting. antenna, has an effective aperture of 500 $c{m}^2$. The total power recived by the antenna is

• A. 10$\mu W$
• B. 20 $\mu W$
• C. 1 $\mu W$
• D. 100 $\mu W$

Answer 1

The correct option is D 100 $\mu W$

Ans : (d)

Intensity of EM wave at 100 m away

= $\frac{251}{4\pi \times {100}^2}W/m^2$

Effective aperture = 500 $c{m}^2=500\times {10}^{-4}{m}^2$

Power = $\frac{251}{4\pi \times 100\times 100}\times 500\times {10}^{-4}$ watt

= 100$\mu W$