# How Does Polarization by Reflection Determine the Refractive Index of Glass?

• fkf
In summary, unpolarized light at an angle of 37.5 ° is reflected off a plan glass surface and its polarization is examined by a Polaroid. The ratio between maximum and minimum intensity from Polaroid when it is rotated around is 4.0. The relevant equations are Fresnel's equations and the question may be more suitable for the homework help forum.
fkf
Unpolarized light falls on an angle of 37.5 ° with a plan glass surface. The reflected light polarization is examined with a Polaroid. The ratio between maximum and minimum intensity from Polaroid when it is rotated around is 4.0. Which is the refractive of index glass?

I would like to use the equation which relates the Intensity with the incident angles with the refraction angle. But doesn't really find out how.

Last edited:
DrDu said:
The relevant equations are Fresnel's equations:
http://en.wikipedia.org/wiki/Fresnel_equations
Are you sure that this question is not more apt for the homework help forum?

Oh sorry, of course. Wont happen again. Thank you.

Since the OP has posted the question in the homework forums, I am locking this thread.

The polarization by reflection phenomenon occurs when unpolarized light is incident on a surface at a certain angle, resulting in the reflected light becoming polarized. In this scenario, the incident angle is 37.5° with a plan glass surface. This means that the angle of incidence, θi, is equal to 37.5°.

To determine the refractive index of the glass, we can use the equation n = sin(θi)/sin(θr), where n is the refractive index of the glass, θi is the angle of incidence, and θr is the angle of refraction. In this case, we need to rearrange the equation to solve for n:

n = sin(θr)/sin(θi)

To find θr, we can use the law of reflection, which states that the angle of reflection, θr, is equal to the angle of incidence, θi. Therefore, θr = 37.5°.

Substituting this value into the equation, we get:

n = sin(37.5°)/sin(37.5°)

Using a calculator, we can determine that sin(37.5°) = 0.6. Therefore, the refractive index of the glass is:

n = 0.6/0.6 = 1

This means that the refractive index of the glass is 1.

We are also given the information that the ratio between the maximum and minimum intensity from the Polaroid when it is rotated around is 4.0. This can be explained by Malus' law, which states that the intensity of polarized light passing through a polarizer is proportional to the square of the cosine of the angle between the polarizer and the polarization direction of the light. In this case, the angle between the polarizer and the polarization direction is 90° when the polarizer is rotated. Therefore, the intensity of the light passing through the Polaroid is 0 when the polarizer is perpendicular to the polarization direction, and maximum when the polarizer is parallel to the polarization direction. This results in a ratio of 4.0 between the maximum and minimum intensity.

In conclusion, the refractive index of the glass in this scenario is 1, and the observed ratio between maximum and minimum intensity from the Polaroid is due to Malus' law.

## 1. What is polarization by reflection?

Polarization by reflection is a phenomenon where light waves that are incident on a surface at a specific angle become polarized, meaning that the light waves oscillate in a specific direction. This occurs when light reflects off a non-metallic surface such as glass, water, or plastic.

## 2. How does polarization by reflection occur?

When light waves hit a non-metallic surface, they are absorbed and then re-emitted in all directions. However, when the angle of incidence is specific, the light waves are mostly reflected in a single plane, leading to polarization. This is known as Brewster's angle.

## 3. What is the difference between linear and circular polarization by reflection?

In linear polarization, the electric field of the light waves oscillates in a single direction, while in circular polarization, the electric field rotates around the axis of propagation. This can be achieved through different angles of incidence on the reflecting surface.

## 4. What are some real-life applications of polarization by reflection?

Polarization by reflection has various applications, including glare reduction in sunglasses, 3D movie technology, and polarizing filters used in photography and microscopy. It is also used in LCD screens to control the brightness and color of pixels.

## 5. Can polarization by reflection be reversed?

Yes, polarization by reflection can be reversed by reflecting the polarized light off another surface at the same angle. This is known as polarization reversal or depolarization. It can also occur naturally when polarized light reflects off a rough surface.

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