A transparent object that has reflecting surfaces and that separates white light that passes through it into different colours is called a prism. It is a wedge-shaped body made from a refracting medium which is bounded by two plane faces inclined to each other with some angle. The angle included between these two faces is known as the angle of a prism or refracting angle and the two plane faces are known as refracting faces. Prism has the traditional triangular shape with a triangular base and rectangular sides. One of the most recognizable uses of the prism consists of dispersing a beam of white light into its component colours. This application is used by spectrographic component and refractometer. Prism can be made from any material that is transparent to the wavelength typical materials like glass, plastic, and fluorite. A dispersive prism can be used to break light into spectral colours. It can be used for reflecting the light, or to split light into the component with different polarization. Prisms have been used in, "folding" the system into a smaller space, "bending" light within a system, changing the orientation of an image, as well as combining or splitting optical beams with partial reflecting surfaces. We need multiple mirrors to achieve results similar to a single prism. Replacing mirror assemblies is perhaps the most useful application of prisms since they both fold or bend light and change image parity. One prism in the place of several mirrors reduces potential alignment error, increase accuracy and minimizes the size and complexity of the system.

**How Prism Work:**

Dispersion is the phenomenon in which the refractive index of any material varies with the colour of light used or the wavelength. As a result, the different colours of light are refracted differently and they leave the prism at different angles which creates an effect similar to a rainbow. Iridescent materials also show a similar separation, such as a soap bubble. Sometime prisms are used for the internal reflection on the surface. If light hits one of the surfaces at a sufficiently steep angle inside the prism, total internal reflection occurs and the light is reflected. Sometime prism is a useful substitute for a mirror.

**Types of Prism:**

Dispersive Prisms:

**Reflective Prism:Â **

**Beam-splitting Prism:**

**Polarizing Prism:Â **

**Deflecting Prism:**

**Refraction through a glass prism:**

Glass prism:

The ray diagram of glass prism is like a triangle. Sometimes a glass prism is also called as a prism. The incident ray in a glass prism is not parallel to the emergent ray. It drifts from its original path by a certain angle. Now we study in detail how refraction takes place in a glass prism.Â

**Reflection through glass prism:**

So the conclusion is that when a light ray travels through a glass prism, it always bends towards the thicker part of the glass prism. We know that the surface of the prism is not parallel to each other so the emergent ray RN and incident ray LQ are also not parallel. Now, let us extend the incident ray LQ to point M. This extended line is the original path of the incident ray. So, the angle between the original path of the incident ray and the emergent ray is known as the angle of deviation.

**Refractive Index of a prism:**

Dispersion is the phenomenon in which the refractive index of any material varies with the colour of light used or the wavelength. As a result, the different colours of light are refracted differently and they leave the prism at different angles which creates an effect similar to a rainbow. Iridescent materials also show a similar separation, such as a soap bubble. Sometime prisms are used for the internal reflection on the surface. If light hits one of the surfaces at a sufficiently steep angle inside the prism, total internal reflection occurs and the light is reflected. Sometime prism is a useful substitute for a mirror.

Dispersive Prisms:

Glass prism:

The ray diagram of glass prism is like a triangle. Sometimes a glass prism is also called as a prism. The incident ray in a glass prism is not parallel to the emergent ray. It drifts from its original path by a certain angle. Now we study in detail how refraction takes place in a glass prism.Â

So the conclusion is that when a light ray travels through a glass prism, it always bends towards the thicker part of the glass prism. We know that the surface of the prism is not parallel to each other so the emergent ray RN and incident ray LQ are also not parallel. Now, let us extend the incident ray LQ to point M. This extended line is the original path of the incident ray. So, the angle between the original path of the incident ray and the emergent ray is known as the angle of deviation.

Consider the prism given above. In the quadrilateral BDCP, at the vertices B and C both the angles are right angles. Therefore,

âˆ P + âˆ BDC = 180Â° â€¦â€¦â€¦â€¦ (1)

In âˆ† BDC,

Â r_{1Â }+ r_{2}Â + âˆ BDC = 180Â°â€¦â€¦â€¦.. (2)

r_{1Â }+ r_{2 =Â }P â€¦â€¦.. (3)

Now, as the sum of deviation at the two surfaces, we can define the total deviation âˆ….

âˆ… = (i - r_{1}) + (e - r_{2})Â

âˆ… = i + e â€“ A â€¦â€¦â€¦â€¦.. (4)

So, the conclusion is that the angle of deviation depends on the angle of incident.

If the deviation is negligible, the refracted ray becomes parallel to the base of the prism. A minimum deviation is denoted by Dmin which is equal to the angle of deviation, the angle of refraction (e) is equal to the angle of incident (i) i.e. i=e and r1=r2.

From equation (3),

2r = P

r = P/2

Similarly,

From equation (4),

The refractive index (Âµ) of the prism is,

Equation 5 determines the refractive index of the prism. For a prism, whose angle is negligible, Dmin is also very small.

âˆ P + âˆ BDC = 180Â° â€¦â€¦â€¦â€¦ (1)

In âˆ† BDC,

Â r

r

Now, as the sum of deviation at the two surfaces, we can define the total deviation âˆ….

âˆ… = (i - r

âˆ… = i + e â€“ A â€¦â€¦â€¦â€¦.. (4)

So, the conclusion is that the angle of deviation depends on the angle of incident.

If the deviation is negligible, the refracted ray becomes parallel to the base of the prism. A minimum deviation is denoted by Dmin which is equal to the angle of deviation, the angle of refraction (e) is equal to the angle of incident (i) i.e. i=e and r1=r2.

From equation (3),

2r = P

r = P/2

Similarly,

From equation (4),

The refractive index (Âµ) of the prism is,

Equation 5 determines the refractive index of the prism. For a prism, whose angle is negligible, Dmin is also very small.