Question

an electromagnetic radiation point source operates at a 250W power with a 10% efficiency. The average energy density at a point distant 10m from the source is​

Answer 1

Given : Power, P = 250W, Efficiency = 10% and Distance, d = 10 m

To find : The average energy density at a point distant 10m from the source

Solution : We know that the efficiency of power is 10% i.e 250 × 0.1 = 25 W

• Also, intensity is given by formula

$I = P \div 4\pi {d}^{2}$

Where P = Power and d = distance from the source

• Formula of average energy density is given as follows :

$u = I \div c$

I = 25 / 4π×10×10

I = 1 / 16π

• Substituting I value in energy density formula

$u = 0.6 \times {10}^{ - 10}$

Hence, the average energy density at a point distant 10m from the source is 0.6×$10{}^{-10}$