Question

An electric dipole ,of length 1m is operated in air, then the time average power radiated by the antenna assuming that it is excited at its centre by a sinusoidal current of amplitude 200mA at a frequency 1.5MHz, is

• A. 394 mW
• B. $394\mu W$
• C. 192mW
• D. $192\mu W$

Answer 1

The correct option is B $394\mu W$

$P_{rad}=\frac{1}{2}{I}^2{r}_{rad}$

$R_{rad}=80{\pi }^2{\left(\frac{l}{\lambda }\right)}^2$

$\lambda =\frac{c}{f}=\frac{3\times {10}^5}{1.5\times {10}^6}=200m$

$R_{rad}=80{\pi }^2{\left(\frac{1}{200}\right)}^2$

$P_{rad}=\frac{1}{2}(200\times {10}^{-3}{)}^2\times \frac{80{\pi }^2}{(200{)}^2}=3.94\times {10}^{-4}W=394\mu W$