Question

The magnitude of the Poynting vector of a planar electromagnetic wave has an average value of 0.939 W/m^2 . The wave is incident upon a rectangular area, 1.5 m by 2.0 m, at right angles. How much total electromagnetic energy falls on the area during 1.0 minute?

Answer 1

Answer:

47 mW

Explanation:

The average value of the Poynting vector, S = 0.939 W/m² = Intensity of wave, I

S = I S

Also, I = P/A where P = Et, P = power of electromagnetic wave, E = energy of electromagnetic wave in time t and t = time = 1 min = 60 s and A = area = lb since the electromagnetic waves falls on area equal to that of a rectangle.

So, S = Et/A

E = SA/t

= Slb/t

= 0.939 W/m² × 1.5 m × 2.0 m/60 s

= 2.817 W/60 s

= 0.047 W

= 47 mW

So, 47 mW of electromagnetic energy falls on the area in 1.0 minute.