27-05-2017, 02:28 PM
The theory:
Prism
A prism is an optical element. It has polished flat surfaces that refract light. The traditional geometric shape of a prism has a triangular base and two rectangular sides. It is called a triangular prism.
A prism can be made from materials such as glass, plastic and fluorite. It can be used to divide light into its components.
How Prisms Work
When light travels from one medium to another medium, it is refracted and enters the new medium at a different angle. The degree of bending of the light path depends on the angle the incident light beam makes with the prism surface and the ratio between the refractive indices of the two media. This is called Snell's law.
![[Image: gif.latex?i.e%2C%20n%20%3D%5Cfrac%7Bsin%...%5C%3Br%7D]](http://latex.codecogs.com/gif.latex?i.e%2C%20n%20%3D%5Cfrac%7Bsin%5C%3Bi%7D%7Bsin%5C%3Br%7D)
Where, n is the refractive index of the prism material.
I is the angle of incidence.
R is the angle of refraction.
The refractive index of many materials varies with the wavelength of the light used. This phenomenon is called dispersion. This causes the light of different colours to be refracted differently and leave the prism at different angles, creating an effect similar to the rainbow. This can be used to separate a white beam of light into its constituent spectrum of colours.
The relationship between the refractive index (n), the prism angle (A) and the minimum deflection angle (D)
Consider the next triangular prism.
![[Image: 1456296567_triangular-prism.jpg]](http://amrita.olabs.co.in/userfiles/1/1456296567_triangular-prism.jpg)
The angle A between the two refractory surfaces ABFE and ACDE is called the prism angle.
A ray of light suffers two refractions as it passes through a prism. If KL is a monochromatic light that falls on the AB side, it is refracted and travels along LM. Once again it undergoes refraction in M and emerges along MN. The angle through which the emerging ray deviates from the direction of the incident ray is called the deflection angle 'd'.
![[Image: 1456296632_prism-out-line.jpg]](http://amrita.olabs.co.in/userfiles/1/1456296632_prism-out-line.jpg)
As the angle of incidence increases, the angle of deviation 'd' decreases and reaches the minimum value. If the angle of incidence increases, the angle of deviation increases.
A graph is drawn between the angle of incidence (i) and the angle of deviation (d) by taking the angle of incidence (i) along the X axis and the angle of deviation (d) along the Y axis. Be a curved chart.
![[Image: 1456296653_graph.jpg]](http://amrita.olabs.co.in/userfiles/1/1456296653_graph.jpg)
The minimum deviation angle is obtained from the graph. Let D be the minimum deflection angle, then the refractive index (n) of the prism material is calculated using the formula,
![[Image: gif.latex?n%3D%5Cfrac%7Bsin%5Cfrac%7B%28...%7B2%7D%7D]](http://latex.codecogs.com/gif.latex?n%3D%5Cfrac%7Bsin%5Cfrac%7B%28A+D%29%7D%7B2%7D%7D%7Bsin%5Cfrac%7BA%7D%7B2%7D%7D)
Learning outcomes:
• Students understand the operation of a prism.
• Students will be better able to perform the experiment in a real laboratory by understanding the procedure.
Prism
A prism is an optical element. It has polished flat surfaces that refract light. The traditional geometric shape of a prism has a triangular base and two rectangular sides. It is called a triangular prism.
A prism can be made from materials such as glass, plastic and fluorite. It can be used to divide light into its components.
How Prisms Work
When light travels from one medium to another medium, it is refracted and enters the new medium at a different angle. The degree of bending of the light path depends on the angle the incident light beam makes with the prism surface and the ratio between the refractive indices of the two media. This is called Snell's law.
Where, n is the refractive index of the prism material.
I is the angle of incidence.
R is the angle of refraction.
The refractive index of many materials varies with the wavelength of the light used. This phenomenon is called dispersion. This causes the light of different colours to be refracted differently and leave the prism at different angles, creating an effect similar to the rainbow. This can be used to separate a white beam of light into its constituent spectrum of colours.
The relationship between the refractive index (n), the prism angle (A) and the minimum deflection angle (D)
Consider the next triangular prism.
The angle A between the two refractory surfaces ABFE and ACDE is called the prism angle.
A ray of light suffers two refractions as it passes through a prism. If KL is a monochromatic light that falls on the AB side, it is refracted and travels along LM. Once again it undergoes refraction in M and emerges along MN. The angle through which the emerging ray deviates from the direction of the incident ray is called the deflection angle 'd'.
As the angle of incidence increases, the angle of deviation 'd' decreases and reaches the minimum value. If the angle of incidence increases, the angle of deviation increases.
A graph is drawn between the angle of incidence (i) and the angle of deviation (d) by taking the angle of incidence (i) along the X axis and the angle of deviation (d) along the Y axis. Be a curved chart.
The minimum deviation angle is obtained from the graph. Let D be the minimum deflection angle, then the refractive index (n) of the prism material is calculated using the formula,
Learning outcomes:
• Students understand the operation of a prism.
• Students will be better able to perform the experiment in a real laboratory by understanding the procedure.
