A vertically polarized electromagnetic wave is sent through two sheets of polari
ID: 1488098 • Letter: A
Question
A vertically polarized electromagnetic wave is sent through two sheets of polarizing material. The first sheet, A, is oriented so that its transmission axis makes an angle of 30 degrees with the vertical. The second sheet, B, is oriented so that its transmission axis is horizontal. The incident beam has an average intensity I0 and an electric field of peak magnitude E0. A) What is the peak value of the wave's electric field after it goes through polarizer A only in terms of E0? B) What is he average intensity of the wave after it passes through bother polarizers in terms of I0? C)Suppose that the electromagnetic wave (after passing through both polarizers) is focused on a circular area (r = 0.040 m) of a person's leg. What is the average power delivered to the leg if I0= 75 W/m^2? D) Suppose that polarizers A and B are interchanged so that the wave is first incident upon polarizer B and then passes through polarizer A. What is the average wave intensity after passing through both polarizers in terms of the initial average intensity?
Explanation / Answer
by using malus law
Intensity after passing through polarizer is I = Io*cos^2(theta)
Io is the maximum intensity which is directly proportional to Eo^2
A) only the parallel component of E to the transmission axis passes through the polarizer
E = Eo*cos(30) = (1.732/2)*Eo = 0.866 *Eo
B) IA = Io*cos^2(30) = 0.75*Io
IB = IA = 0.75 *Io
C) power P = Io*(pi*R^2) = 75*3.142*0.04*0.04= 0.37704 W
D) IB = Io
IA = IB*cos^2(30) = 0.75*Io