PHYS 1C Lecture Notes - Lecture 14: Total Internal Reflection, Refraction

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7 May 2018

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What happens with a light ray with an incident angle of 60

degrees in glass heading out to air:

Refraction of light

Here the angle doesn't exist. The angle was so great that it refracted the incident ray back

to the first medium (reflected it)

This is known as Total Internal Reflection (TIR)

It can only occur if you move from a slow medium to a fast medium such that the refracted

ray is bent away from the normal compared to the incident ray

Here you can see light ray undergoing total internal reflection

This means that at the angle that light ray hits at, no light enter the second medium

Total internal reflection

We define the critical angle as a particular angle of incidence that will result in an anle fo

refraction of 90 degrees.

For angles of incidence greater than the critical angle, the beam is entirely reflected at the

boundary

This ray will obey the Law of Reflection at the surface boundary

Can we use this to redirect light downwards?

Optical fibers consist of "core" surrounded by "cladding" with ncladding>ncore. Light hits

core-cladding interface. Undergoes total internal reflection and stays in the fiber

○

This is how fiber optics works!

(14) Lecture 25B Total Internal Reflection

Sunday, May 6, 2018

12:23 PM

week 6 Page 1

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Document Summary

What happens with a light ray with an incident angle of 60 degrees in glass heading out to air: The angle was so great that it refracted the incident ray back to the first medium (reflected it) This is known as total internal reflection (tir) It can only occur if you move from a slow medium to a fast medium such that the refracted ray is bent away from the normal compared to the incident ray. Here you can see light ray undergoing total internal reflection. This means that at the angle that light ray hits at, no light enter the second medium. We define the critical angle as a particular angle of incidence that will result in an anle fo refraction of 90 degrees. For angles of incidence greater than the critical angle, the beam is entirely reflected at the boundary. This ray will obey the law of reflection at the surface boundary.

Related Questions

1)A light ray is incident on a reflecting surface. If the light ray makes a 25° angle with respect to the normal to the surface, what is the exact angle (in degrees) made by the reflected ray relative to the normal?

2)The light ray that makes the angle θ1' is the refracted ray (true or false?)

3)True or False: The Law of Reflection can be used to show how an image appears behind a mirror and it can also be used to determine where the image will be located.

4) Snell's law is another name for the

law of dispersion

law of reflection

law of refraction

5) A light ray incident on a block of glass makes an incident angle of 50.0° with the normal to the surface. The refracted ray in the block makes a 26.8° with the normal. What is the index of refraction of the glass?

A light ray traveling from a higher index of refraction medium into a lower index of refraction medium (for example, from water into the air) would bend away from the normal to the medium surface. When the refracted ray is parallel to the boundary of the medium, θ2= 90°. The incident angle, θ1, becomes θc, called the

viridianchinchilla179

1. A light ray is incident on a reflecting surface. If the light ray makes a 25° angle with respect to the normal to the surface, what is the exact angle (in degrees) made by the reflected ray relative to the normal?

2. The light ray that makes the angle θ₁' is the refracted ray (true or false?)

3. True or False: The Law of Reflection can be used to show how an image appears behind a mirror and it can also be used to determine where the image will be located.

4. Snell's law is another name for the

law of dispersion
law of reflection
law of refraction

5. A light ray incident on a block of glass makes an incident angle of 50.0° with the normal to the surface. The refracted ray in the block makes an 26.8° with the normal. What is the index of refraction of the glass?

6. A light ray traveling from a higher index of refraction medium into a lower index of refraction medium (for example, from water into air) would bend away from the normal to the medium surface. When the refracted ray is parallel to the boundary of the medium, θ₂= 90°. The incident angle, θ₁, becomes θ_c, called the

cauchy angle
critical angle
conjugate angle
classic angle

pearchinchilla839

In Example 33.11, the water-glass interface is horizontal. If instead this interface were tilted 15.0° above the horizontal, with the right side higher than the left side, what would be the angle from the vertical of the ray in the glass? (The ray in the water still makes an angle of 60.0° with the vertical).

EXAMPLE 33.11: Reflection and refraction

In Fig 33.11, material a is water and material b is a glass with an index of refraction 1.52. If the incident ray makes an angle of 60.0° with the normal, find the directions of the reflected and refracted rays.

SOLUTION

IDENTIFY: This is a problem in geometric optics. We are given the incident angle and the index of refraction of each material, and we need to find the reflected and refracted angles.

SET-UP: Figure 33.11 shows the rays and angles for this situation. The target variables are the reflected angle θ_r and the refracted angle θ_b. Since n_b is greater than n_a, the refracted angle must be smaller than the incident angle θ_a; this is shown in the figure.

EXECUTE: According to Eq 33.2, the angle the reflected ray makes with the normal is the same as that of the incident ray so θ_r= θ_a=60.0°.

To find the direction of the refracted ray, we use Snell’s law, Eq 33.4, with n_a=1.33, n_b=1.42, and θ_a=60.0°. We find:

EVALUATE: The second material has a larger refractive index than the first, just like the situation shown in Fig 33.8a. Hence, the refracted ray is bent toward the normal as the wave slows down upon entering the second material and θ_b< θ_a.

Figure 33.11. Reflection and refraction of light passing from water to glass

Figure 33.8. Reflection and refraction in three cases. (a) Material b has a larger index of refraction than material a. (b) (a) Material b has a smaller index of refraction than material a. (c) The incident light ray is normal to the interface between the materials.