Register to reply 
Intensity of light with given power through a polarizer 
Share this thread: 
#1
Apr1410, 10:28 PM

P: 190

1. A 200 mW horizontally polarized laser beam passes through a polarizing filter whose axis is 25 degrees from vertical.
2. Malus's Law 3. Ok, so I will use theta = 65 degrees in the I = I_{0}cos(theta) equation, right? But how do I calculate I_{0} knowing only power and not area? 


#2
Apr1510, 12:29 AM

HW Helper
Thanks
P: 10,634

How is the intensity of light defined? And what does Malus's Law say? The equation you use is wrong.
ehild 


#3
Apr1510, 08:03 PM

P: 190

I = P/A = 0.5c*ep_{0}*E^{2}
And Malus's law states that the intensity of the light transmitted is the product of the intensity of the incident light and the square of the cosine of the angle theta with respect to the polarizer's axis. I don't get what you're getting at.... In terms of the theta I use, this is how I am thinking about it: I would use 25 degrees if the incident light was vertically polarized. Since it is horizontally polarized, i.e. is at 90 degrees, I should use 9025 = 65 degrees... 


#4
Apr1510, 11:41 PM

HW Helper
Thanks
P: 10,634

Intensity of light with given power through a polarizer
It is all right if you use the square of the cosine, but you wrote I=Io*cos(theta) in the previous post.
As for intensity, it is power/area. The incident power of the laser beam is given and the area is the same before and after crossing the polarizer. You did not write what is the question, but presumably it is the power of the laser beam after the polarizer. ehild 


Register to reply 
Related Discussions  
Intensity and Power  Introductory Physics Homework  4  
Need help to gradually ramp up/down intensity of LED at poweron/poweroff  Electrical Engineering  2  
Why does light intensity decrease when light passes through a glass block?  General Physics  7  
Intensity of light / measuring wavelength of light  Introductory Physics Homework  2  
Circularly polarized light through a linear polarizer  Advanced Physics Homework  9 