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What is the amount of Electric field present at a distance of 10km for an isotropic radiator with radiating power 3kW?(a) 30mV/m(b) 60mV/m(c) 15mV/m(d) 10mV/mI got this question in examination.My question comes from Isotropic Radiators topic in portion Antenna Parameters of Antennas

Answer»

Right option is (a) 30mV/m

Explanation: For ISOTROPIC radiator, power per unit area = \(\frac{P_t}{4πr^2}\) — (1)

From pointing THEOREM, \(P=\frac{\mid E_{max}^2\mid}{2\eta}\), where η=120π. —– (2)

Equating (1) & (2) and Erms=Emax/√2, we get

\(E_{rms}=\frac{\SQRT{30P_t}}{r}=\frac{\sqrt{30×3000}}{10000}=30mV/m.\)



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