Refraction of Light

Refraction Definition

Refraction is the bending of a wave when it enters a medium where its speed is different. We can define it as:

Refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium

Refraction of light is one of the most usually observed phenomena which includes refraction of light through prism, but other waves like sound waves and water waves also experience refraction.

Laws of Refraction of Light

Laws of refraction state that:

  • The incident ray, refracted ray, and the normal to the interface of two media at the point of incidence all lie on the same plane.
  • The ratio of sine of angle of incidence to the sine of angle of refraction is a constant. This is also known as Snell’s law of refraction.
    \(\frac{sin\;i}{sin\;r}=constant\)

Causes of Refraction

The cause of refraction of light is as follows:

  • The frequency of the refracted ray remains constant.
  • Due to partial reflection and absorption of light at the interface, the intensity of the refracted ray will be less than the incident ray.
  • When the light crosses the boundary between two different media, deviation of light occurs resulting in refraction such that there is a change in wavelength and speed of light.

Effects of Refraction

  • Twinkling of stars is due to refraction of light.
  • Mirage and looming are the optical illusion which are result of refraction of light.
  • A swimming pool always looks shallower than it really is because the light coming from the bottom of the pool bends at the surface due to refraction of light.

Refraction Examples

  • Formation of rainbow is an example of refraction as the sun rays bend through the raindrops resulting in rainbow.
  • Prism is also an example of refraction.

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What is Refraction of Light in Ray Optics?

Refraction of light refers to the change in direction of a ray of light when it travels from one medium to another. Refraction of light is one of the most common types of phenomenon  but various other waves like water waves and sound waves also experience refraction.

Example:

For example, the figure below shows a ray of light travelling from a medium of air to that of water.

Refraction of Light

Ray of light travelling from air to water

Have u ever soaked your legs in a bucket?

You would have noticed that your legs looked slightly deformed and kind of shorter. The phase velocity of travelling light rays are altered when they travel from one medium to another of a different refractive index.

What is Refractive Index?

Refractive index also called the index of refraction describes how fast light travels through the material.

Refractive Index is dimensionless. For a given material, the refractive index is the ratio between the speed of light in a vacuum (c) and the speed of light in the medium (v). If the refractive index for a medium is represented by n, then it is given by the following formula:

\(~~~~~~~\) \( n = \frac {c}{v} \)

Based on the refractive index of the medium, the light ray changes its direction, or it bends at the junction separating the two media. If the light ray travels from a medium to another of a higher refractive index, it bends towards the normal, else it bends away from the normal.

Applications of Refraction of Light

Refraction has many applications in optics and technology. Depending on the type of spherical lens used (convex or concave) refraction through glass has many uses.

  • A lens uses refraction to form an image of an object for various purposes, such as magnification.
  • Passing white light through a glass prism can split the white light into the spectrum of colour (VIBGYOR).
  • In nature, it is refraction that causes us to see a different phenomenon like mirages and also the twinkling of stars… which is caused due to the atmospheric refraction of light.

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