Question

The magnitude of the Poynting vector of a planar electromagnetic wave has an average value of 0.724 W/m^2. What is the maximum value of the magnetic field in the wave?

a. 77.9 nT
b. 55.1 nT
c. 38.9 nT
d. 108 nT

Answer 1

A I think : )

Step-by-step explanation:

Answer 2

a. 77.9 nT

Step-by-step explanation:

Given;

average value of the electromagnetic wave, E = 0.724 W/m^2

The average value of a Poynting vector is given by;

`S = (1)/(2\mu_o) *E_oB_o\\\\But, E_o = cB_o\\\\S = (1)/(2\mu_o) *cB_o^2\\\\cB_o ^2= 2\mu_o S\\\\B_o^2 = (2\mu_o S)/(c)\\\\B_o = \sqrt{ (2\mu_o S)/(c)} \\\\B_o = \sqrt{ (2(4\pi*10^(-7)) (0.724))/(3*10^8)}\\\\B_o = 7.79*10^(-8) \ T\\\\B_o = 77.9*10^(-9) \ T\\\\B_o = 77.9 \ nT`

Therefore, the maximum value of the magnetic field in the wave is 77.9 nT.