# Optical Prism: Refractive Index & Light Rays

• princemartin1
In summary, the question asks for the required refractive index of the surrounding medium (n1) to allow light with longer wavelengths than 656.3 nm to exit the prism along a specific path (path 2), while light with shorter wavelengths is reflected along another path (path 3). This can be determined by using Snell's law and understanding that longer wavelengths will exit through path 2, while shorter wavelengths will follow path 3. The normal to the prism is not relevant in this scenario.
princemartin1
MODERATOR'S NOTE: THIS THREAD HAS BEEN MOVED HERE FROM ANOTHER FORUM, SO THERE IS NO TEMPLATE

A ray of white light is incident on a 45o – 90o – 45o prism (ray 1 in the figure on the left). The prism is

constructed from crown glass with a refractive index of n2 = 1.5205 at the wavelength of the Fraunhofer C line (656.3 nm).

What would be the required refractive index of the surrounding medium (n1) to allow light at longer wavelengths than 656.3 nm to exit the prism along path 2 while light at shorter wavelengths is reflected along path 3.

Last edited by a moderator:
princemartin1 said:
(ray 1 in the figure on the left).
No figure, no prism orientation, no incidence angle --- we do need the rest of the question.

Bystander said:
No figure, no prism orientation, no incidence angle --- we do need the rest of the question.

princemartin1 said:
That's progress. Next, you need to post any equations you have been taught that you deem may be relevant, and an attempt at solution.

haruspex said:
That's progress. Next, you need to post any equations you have been taught that you deem may be relevant, and an attempt at solution.
• I have snell's law : n sin theta 1 = n2 sin theta 2

princemartin1 said:
• I have snell's law : n sin theta 1 = n2 sin theta 2
Ok, but the refractive index depends somewhat on wavelength. You are given the refractive index for a particular wavelength, and you want longer wavelength light to pass through but shorter wavelengths to be internally reflected. That being the case, where do you think light of the given wavelength will go?

haruspex said:
Ok, but the refractive index depends somewhat on wavelength. You are given the refractive index for a particular wavelength, and you want longer wavelength light to pass through but shorter wavelengths to be internally reflected. That being the case, where do you think light of the given wavelength will go?
It will exit through 2 and also the normal has to pass through the point 2 and 3

princemartin1 said:
It will exit through 2 and also the normal has to pass through the point 2 and 3
Longer wavelengths than 656.3nm will exit along paths like path 2, while those shorter will take path 3. But what will a wavelength of exactly 656.3 do?

By the way, you need to understand that 'path 2' is only illustrative. All wavelengths longer than 656.3 will exit that face of the prism, but at different angles depending on the wavelength. Shorter wavelengths, on the other hand, will follow exactly path 3.

I didn't understand your remark about the normal. Normal to what? '2' and '3' are not points, they are paths.

## 1. What is an optical prism?

An optical prism is a transparent object with flat surfaces that refracts or bends light rays. They are typically made of glass or plastic and come in a variety of shapes, such as triangular, rectangular, or hexagonal.

## 2. What is the refractive index of an optical prism?

The refractive index of an optical prism is a measure of how much the light is bent as it passes through the prism. It is typically denoted by the symbol "n" and is a ratio of the speed of light in a vacuum to the speed of light in the material of the prism.

## 3. How does an optical prism work?

An optical prism works by refracting or bending light as it passes through the prism. This is due to the change in speed of light as it travels from one material (such as air) to another (such as glass) with a different refractive index. The angle at which the light is bent depends on the shape and refractive index of the prism.

## 4. What is the difference between a convex and concave optical prism?

A convex optical prism is thicker at the center and thinner at the edges, causing light rays passing through it to converge. A concave optical prism, on the other hand, is thinner at the center and thicker at the edges, causing light rays to diverge. This results in different effects on the light passing through the prism.

## 5. What are some real-world applications of optical prisms?

Optical prisms have many practical applications in our daily lives. They are used in cameras and lenses to correct and focus light, in binoculars and telescopes to magnify images, in microscopes to view tiny objects, and in spectroscopes to separate and analyze different wavelengths of light. Prisms are also used in optical instruments such as periscopes, kaleidoscopes, and surveying equipment.

### Similar threads

• Introductory Physics Homework Help
Replies
4
Views
546
• Introductory Physics Homework Help
Replies
2
Views
1K
• Introductory Physics Homework Help
Replies
13
Views
3K
• Introductory Physics Homework Help
Replies
1
Views
1K
• Introductory Physics Homework Help
Replies
11
Views
2K
• Introductory Physics Homework Help
Replies
3
Views
1K
• Introductory Physics Homework Help
Replies
22
Views
2K
• Optics
Replies
9
Views
294
• Introductory Physics Homework Help
Replies
6
Views
4K
• Introductory Physics Homework Help
Replies
4
Views
1K