Determine the rms value of the electric field of the transmitted beam

[EmoryGirl]

Homework Statement

A beam of polarized light has an average intensity of 13.2 W/m2 and is sent through a polarizer. The transmission axis makes an angle of 27.5° with respect to the direction of polarization. Determine the rms value of the electric field of the transmitted beam.

Homework Equations

The Attempt at a Solution

This is what I have done to try this problem:
I used E_rms = square root of: [I(4pi * 10^-7)(3 x 10^8)]
I used I = Iocos^2theta
I = (13.2)(cos27.5)^2
I = 10.3856

According to the homework program I am using, the answer I have gotten is not correct...I am not sure what I am doing wrong. Thanks in advance!

 

[Redbelly98]

I agree with your value of I=10.4 W/m^2.
Can you post your calculation of E_rms?

 

[EmoryGirl]

I have finally solved it! So my E_rms equation was correct. My intensity was not...
Turns out what I had to do was not square the cos...
so instead of I = I_ocos²27.5
the equation is:
I = I_ocos27.5 = 11.7085

Which I can then plug into the equation for E_rms above

Thanks for your help!

 

[Redbelly98]

Okay, but you are supposed to square the cosine when dealing with the intensity:

http://en.wikipedia.org/wiki/Malus's_law#Malus.27_law_and_other_properties

 

[EmoryGirl]

yeah, I know...but our homework is on a computer program (CAPA), and after using 7 out of 10 tries on this problem I called a classmate and he said that he did it without the cos squared...so I tried it and it was finally marked correct!...not really sure what's going on with this problem!