Laws of Refraction of Waves

Refraction of Waves:

When a progressive wave traveling in a homogeneous medium meets a surface of separation with another homogenous medium, part of the incident wave is transmitted into the second medium. This phenomenon is known as the refraction of waves. In refraction, generally, the refraction of wave motion changes while the waves cross the interface of two media.

If nearly all of the energy carried by the incident wave enters the second medium, the second medium is called a transparent medium. For light waves, air water, glass, etc. are transparent media.

On the other hand, if a negligible portion of the energy enters the second medium, the second medium is called an opaque medium. For light waves, wood, iron, brick walls, etc. are opaque media. Between them, ground glass, oily paper, etc. are semi-transparent media.

Laws of Refraction:

Refraction of waves obeys the following into two laws:

1. The incident ray, the refracted ray, and the normal to the refracting surface at the point of incidence lie in the same place.

2. The ratio of the sine of the angle of incidence to the sine of the angle of the refraction is constant. The magnitude of the constant depends on the nature of the two media and the color of the incident wave.


sin i/sin r = constant (1μ2)

where i and r are the angle of incidence and the angle of refraction, respectively, and μ is called the refractive index of the second medium with respect to the first medium.

The second law of refraction is known as Snell’s Law.