Snell’s Law: Experiment, Exceptions & Law of Refraction

Refraction is considered as a process of bending of light rays whenever light travels from any transparent medium to another medium, the transparent medium includes air, water, and sunlight. Refraction plays an important role in our daily life as it helps in the construction of various optical objects such as microscopes, telescopes, glass prisms, and magnifying glasses. Refraction also helps in the formation of rainbows as whenever sunlight refracts through water droplets in the air, then it forms a rainbow.  The process through which we can observe various natural phenomenons occurring is the refraction of light. It works on Snell's law, but before understanding this law in detail, we begin with the basics of refraction.

Keyterms: Refraction, light rays, rainbow, microscopes, telescopes, glass prisms, magnifying glasses, Snell's law, air, water, sunlight

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What Causes Refraction?

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Refraction of the object is determined by the refractive index of the medium, through which light passes, and that depicts the behaviour in that medium. The change in direction of light occurs on traveling from one substance to substance and has to face a change in speed that is dependent upon the refractive index of the material. For example, as we know air is much denser than water, so whenever the light passes from air to water, then the speed of light will slow down, which will cause a change of direction in the water. 

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Law of Refraction(Snell’s Law)

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In 1962, Willebrord Snell discovered the laws of reflection which are popularly known as Snell’s law. As we have seen above, whenever light passes through one medium to another medium, then the refraction takes place and the degree of refraction can be predicted with the help of snell’s law. One should have great knowledge about refraction and properties of refraction

Snell’s law is a law that whenever a ray of light or waves passes through two isotopes i.e. air, water, or glass then this law is commonly used to find the relationship between the angle of incidence and the angle of refraction. This law also states that normal to the boundary between the two transparent objects, then the refracted way and the ray of incidence will lie on the same plane. The speed of light in the vacuum will be 3.00 x 10 s m/s.

This law is mainly used in optical science, to compute the angle of incidence and refraction and the aim is to calculate the refractive index of an object. The indices of refraction namely n₁ and n₂ help in representing the factors by which rays of light decrease, when a ray of light is traveling through a refractive medium.

Whenever light passes through two isotopes, depending upon the refractive indices of the two objects, then the light will either be refracted to a higher degree or a lower angle. The angles will be calculated based on the normal line, which will be perpendicular to the boundary of the object. If the light is traveling from air to water, then it will be reflected towards the normal line as light is slowed down in the water and in the case when light is traveling from water to air, then it would reflect away from the normal line.

Refractration between two surfaces will be reversible as if all the conditions were identical, then the angle will be equivalent for light falling in the opposite direction. 

Snell’s law can be expressed in the ratio of the wavelength of two media, i.e. n₁ and n₂

sinθ₁/Sinθ₂ = v₁/v₂=n_i/n₂

Snell’s Law: Experiment

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The Law of refraction can be explained with the help of an experiment

Aim: To measure the path of light rays when it passes through a rectangular slab(made up of glass), Measuring the various angles: Angle of incidence, angle of emergence, and the angle of refraction, and finding a relationship between these angles.

Requirement of materials for performing this experiment: A normal sheet of white paper, a drawing board,5-6 paper pins, a rectangular glass slab, a protractor to measure the angles, and thumb pins.

Steps:

• The first step is to take a white sheet and fix it on the drawing board with the usage of thumb pins which will allow the sheet to remain in its position.
• Take a rectangular glass slab and place it on the centre position of the white sheet and mark its outline boundary with the help of a pencil and name the rectangular figure obtained as ABCD.
• Choose one side of the figure, AB and take a point E and construct a perpendicular and name it as EN and mark it as a normal ray.
• With the usage of a protractor, draw an angle of 30 degrees with the perpendicular EN and fix two paper pins and name it as P and Q on the ray of the angle created.
• Look through a rectangular glass slab from another side, CD, and attach pins R and S such that P, Q, R, S should lie in a straight line.
• Connect Points R and So so that it meets at CD, and mark the point as F
• Measure the angles formed at AB and CD.

Conclusion: The angle of incidence is approximately the same as the angle of emergence and whenever the light rays travel from rarer medium(Air) to denser medium(Glass), then the light will bend towards the normal 

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