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’s path depends on the angle that the incident beam of light makes with the surface of the prism, and on the ratio between the refractive indices of the two media. This is called Snell’s law or law of refraction.

$$n=\frac{\sin i}{\sin r}$$

where, 𝑛 is the refractive index of the material of the prism.

𝑖 is the angle of incidence.
𝑟 is the angle of refraction.

Refraction Through a 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.

The angle 𝐴 between the two refracting surfaces is called the angle of the prism. In the above figure, a ray of light suffers two refractions on passing through a prism. If KL is a monochromatic light falling on the side AB, it is refracted and travels along LM. It once again suffers refraction at M and emerges out along MN. The angle through which the emergent ray deviates from the direction of the incident ray is called as the angle of deviation 𝑑.

As the angle of incidence increases, the angle of deviation decreases and reaches a minimum value. If the angle of incidence is further increased, the angle of deviation increases.

The angle of minimum deviation is obtained from the graph. Let 𝐷 be the angle of minimum deviation, then the refractive index (𝑛) of the material of the prism is calculated using the formula, $$n=\frac{\sin \left(\frac{A+D}{2}\right)}{\sin \left(\frac{A}{2}\right)}$$

Requirements for this Science Experiment

⦁ Prism ⦁ White Paper ⦁ Pencil ⦁ Protractor ⦁ Pins