Intensity of unpolarized light through two polarizers

In summary, the conversation discusses the effects of passing unpolarized light through two polarizing filters with different orientations. According to Malus's Law, the intensity of the light should be reduced by half after passing through the first filter, and then further reduced by a factor of cos(theta) after the second filter. However, there is a discrepancy in the calculated intensity and the relationship between electric field and intensity is also mentioned. The speaker suggests focusing on the ratio between quantities rather than brute force calculations.
  • #1
Linus Pauling
190
0
1. Unpolarized light with intensity 440 W/m2 passes first through a polarizing filter with its axis vertical, then through a polarizing filter with its axis 20.0 degrees from vertical.



2. Malus's Law



3. Ok, the intensity after going through the first polarizer should be 1/2 the original. This, after the second polarizer, I = 220*cos20) = 207 W/m2, which is incorrect.
 
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  • #2
The filter works by allowing only the parallel component of the electric field, E cos(theta), through. How are the electric field of the light and the intensity of the light related?
 
  • #3
I = P/A = 0.5c*epsilon_0*E^2

Again, I don't see how to get I from P without knowing A.
 
  • #4
You're getting too caught up in just brute force calculation when you should be focusing on how one quantity depends on another. You don't need to know P or A. Think ratios.
 

FAQ: Intensity of unpolarized light through two polarizers

1. What is the definition of intensity of unpolarized light?

The intensity of unpolarized light refers to the amount of light energy passing through a specific area in a given amount of time. It is a measure of the brightness or strength of light.

2. What are polarizers and how do they affect the intensity of unpolarized light?

Polarizers are filters that only allow light waves with a specific orientation to pass through. When unpolarized light passes through a polarizer, it becomes partially polarized, meaning the light waves are aligned in a specific direction. This results in a decrease in the intensity of the light passing through the polarizer.

3. How does the angle of the polarizers affect the intensity of unpolarized light?

The angle of the polarizers determines the amount of polarized light that can pass through. When the polarizers are aligned at 90 degrees to each other, no light can pass through, resulting in the lowest intensity. As the angle decreases, more light can pass through, resulting in an increase in intensity.

4. Can the intensity of unpolarized light passing through two polarizers be calculated?

Yes, the intensity of light passing through two polarizers can be calculated using the Malus' Law. This law states that the intensity of light passing through two polarizers is equal to the initial intensity of unpolarized light multiplied by the cosine squared of the angle between the polarizers.

5. How does the material of the polarizers affect the intensity of unpolarized light?

The material of the polarizers determines the wavelengths of light that can pass through. Some materials may only allow certain wavelengths to pass through, resulting in a decrease in intensity. Additionally, the quality and thickness of the material can also affect the intensity of light passing through.

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