[ف.نووي]

At a distance of 10 km from a radio transmitter, the amplitude of the E-field is 0.20 volts/meter. What is the total power emitted by the radio transmitter?
a. 10 kW b. 67 kW c. 140 kW
d. 245 kW e. 21 kW
solution:

S=POWER/area=P/(4πr^2 )----->P=4πr^2 S

But S=(E_m^2)/(2Cµ_0 ) ---->→P=(2πr^2 E_m^2)/(Cµ_0 )=
(2πr^2 E_m^2)/(Cµ_0 )=(2π×((10^4)^2×(0.2)^2)/(4π×10^(-7)×3×10^8 )=67kW