Concise Selina Solutions for Class 10 Physics Chapter 4 Refraction of Light at Plane Surfaces


The change in the direction of the path of light, when it passes from one transparent medium to another transparent medium, is called refraction.

Refraction of light is essentially a surface phenomenon.

Refraction is caused because of the change in the speed of light from one medium to another.

When a ray of light enters a denser medium it is refracted towards normal in such manner than the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant, this constant being called the refractive index n.

  • The first law of refraction states that the incident ray, the refracted ray and the Normal at the point of incidence, all lie in the same plane.
  • The second law of refraction states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for the pair of media in contact. The second law of refraction is also known as Snell’s law of refraction.

Refractive Index: - The ratio of the speed of light in a vacuum to the speed of light in the medium is defined as refractive index ‘n’. It is called the absolute refractive index.