Polarization by reflection and Brewsters Angle

In summary, the index of refraction of an unknown liquid can be computed by observing the behavior of a beam of light reflected off its surface and examined with a linear sheet polarizer. By tilting the polarizer at an angle of 54.3 degrees and ensuring that the transmission axis is parallel to the plane of interface, the light is completely passed through the polarizer. This angle is equivalent to the Brewster angle, which is also the angle of reflection, and can be used to solve for the index of refraction using the equation tan θp = nt/ni. Using a different angle, such as 35.7 degrees, would result in a value less than one and may not make sense in this context.
  • #1
Sswift
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Homework Statement



A beam of light is reflected off the surface of some unknown liquid, and the light is examined with a linear sheet polarizer. It is found that when the central axis of the polarizer (that is, perpendicular to the plane of the sheet) is tilted down from the vertical at an angle of 54.3 Degrees,the reflected light is completely passed provided the transmission axis is parallel to the plane of interface. From this information, compute the index of refraction of the liquid.

Homework Equations


tan θp=nt/ni
ni≈1

The Attempt at a Solution



So I think that the since the light is completely passed through the polarizer that my angle θp is just the 54.3 degrees that the polarizer is tilted at, but when I draw up what I believe to be happening I think that brewsters angle which is also the angle of reflection is 35.7 degrees rather than 54.3. But if I was to plug this into the equation above and solve for nt I get a value less than one. Using 54.3 degrees gives me an answer that makes sense. I'm just not sure why I use that angle, any help?
 
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  • #2
Sswift said:
So I think that the since the light is completely passed through the polarizer that my angle θp is just the 54.3 degrees that the polarizer is tilted at, but when I draw up what I believe to be happening I think that brewsters angle which is also the angle of reflection is 35.7 degrees rather than 54.3.

Why do you think the Brewster angle is 35.7 degrees rather than 54.3 degrees?
 

Related to Polarization by reflection and Brewsters Angle

1. What is polarization by reflection?

Polarization by reflection is a phenomenon where light waves that are incident on a smooth surface at a particular angle become polarized. This means that the light waves vibrate in a single plane as they are reflected, instead of vibrating in all directions like unpolarized light.

2. What is Brewster's Angle?

Brewster's Angle is the angle of incidence at which light waves become completely polarized during reflection. It is defined as the angle at which the reflected ray and the refracted ray are perpendicular to each other. At Brewster's Angle, the reflected light is completely polarized in a direction parallel to the reflecting surface.

3. Why does polarization by reflection occur?

Polarization by reflection occurs because of the properties of light waves. Light waves are transverse waves, meaning they vibrate perpendicular to the direction of propagation. When light waves are incident on a smooth surface at a particular angle, the vibrations in one direction are absorbed by the surface, while the vibrations in the perpendicular direction are reflected, resulting in polarized light.

4. What are the applications of polarization by reflection?

Polarization by reflection has various applications in everyday life, such as in sunglasses and polarizing filters for photography. It is also used in optical instruments, such as polarimeters, and in the production of 3D movies. In addition, polarization by reflection is important in understanding the reflection of light from non-metallic surfaces, such as glass and water.

5. How does changing the angle of incidence affect polarization by reflection?

The degree of polarization by reflection depends on the angle of incidence. At Brewster's Angle, the reflected light is completely polarized, but at other angles, the degree of polarization is less. As the angle of incidence deviates from Brewster's Angle, the degree of polarization decreases until it reaches a minimum at 90 degrees. Beyond 90 degrees, the reflected light becomes unpolarized again.

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