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Refraction

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 Sub Topics The process of bending light waves are called refraction. Like reflection, refraction can occur with any kind of wave. Refracted waves do not bounce back. Instead, they continue going forward, but in a new direction. As with reflected light waves, refracted light waves help us to see things. refraction in our eyes focuses light waves so that our eyes see object clearly. In eyeglass lenses, refraction helps correct vision problems. In a camera lenses, it focuses an image to make a photograph. Refraction even causes the rainbow that arches across the sky at the end of a thunderstorm.

Definition

Refraction of light is the phenomenon of charge in the path of light, when it goes from one medium to another. When a light travels from one medium to another medium, the speed of the light will change due to the nature of the medium. So the path of the light ray also changes. Hence we can say that bending of light rays takes place.

Causes

The basic cause of refraction is change in the velocity of light in going from one medium to the other. Change in velocity causes the change in the directions of the ray. So the light ray bends according to the nature of the medium. If the light is travels from rarer to denser medium, the refracted ray bend towards the normal. If the light is travels from denser to rarer medium the refracted ray goes away from the normal. This is due to the velocity changes during the propagation of light.

Refraction Index

Index of refraction or refractive index can be defined as how a light ray travels from one medium to another. This is a dimensionless quantity. Index of refraction can be denoted as n. We can calculate this by using the incident and refracted angles as well as by knowing the velocity of the propagation. If we are using the incident angle and refracted angle; is termed as Snell's law.This is given by,

If we are using the velocity of propagation, the formula becomes

where c is the velocity of light in vacuum and v is the velocity in medium.

Law of Refraction

The laws of refraction is mentioned below:

• The incident and refracted rays are on opposite sides of the normal and all the three are in the same plane.
• The ratio of sine of the angle of incidence to the sine of angle of refraction is constant for the part of media in contact. this constant is denoted by the letter n and is called refractive index of the medium two. with respect to medium one.This law is also called Snell's law of refraction.

Negative Refraction

Negative refraction is nothing but the the phenomenon of bending of light in a medium with negative permeability. If a light ray is entering from one medium to another with negative permeability, the refracted ray takes the same direction, but which is refracted through the second medium. The illustrated figure will give clear idea about the negative refraction.

Sound Refraction

Refraction occurs when the speed of the waves changes. The speed of sound waves in air is affected by the air temperature, so if it pass through layers of air at different temperatures they will be refracted or turned in a different direction. On a summer evening when the air near the ground becomes cool, refraction makes it easier to hear distant sounds across the countryside. The sound waves are bent or refracted down towards the ground. This can be explained by showing that the wavefront are further apart in the warm air where the sound travels faster, likewise they are closer together nearer the ground where the sound travels slower in the cooler air. The direction of travel of the sound energy is at right angles to the wavefront this can be seen to bend downwards due to the refraction of the sound waves.

On a day when the ground is very hot and the lower layers of air are the hottest, the sound waves are bent upwards away from the ground making it more difficult to hear over any distance. This effect can be compared with the refraction of light which produces a mirage.

Water Refraction

If we are looking an object which is placed in water, it seems to be appear above the actual depth. This is because of the refraction of light in water. Here air is the first medium and water is the second medium. This can be illustrated in the below figure.

Here the actual depth of the fish is AB, but we can see the fish at A'B'. The observer is standing in the air medium.