Huygen’s Principle states that each and every point on a wavefront serves as a source of wavelets which then spread forward at the same speed. The new wavefront is in a line tangent to all of the wavelets.
It is also known as Huygens-Fresnel principle, named after Christiaan Huygens (Dutch physicist) and Augustin-Jean Fresnel (French physicist). This is used as a method to analyse the problems of wave propagation in the far-field limit and also in the near-field diffraction.
In 1768, Huygens proposed that each and every point which is touched by a luminous disturbance, becomes a source of a spherical wave. The sum total of the waves that are caused due to disturbance (also known as the secondary waves) determine the form of the new wave.
- S= distance
- V= propagation speed (it is the speed of wave which is emitted by each point of the wavefront)
- T= time
The waves that are emitted are semicircular in nature and the new wavefront is tangent to the wavelets. The behaviour of the waves can be counterintuitive. Huygens’ principle of wave analysis helps in understanding the movement of waves that move around the objects.
Eg. Shouting results in spreading of sound in all the directions from that person. But in a closed confinement, like a bedroom with only one door, and then they shout, the sound hits the wall and only the wave heading towards the door into the lobby would go through the door.
Ampere’s law and Faraday’s law fall perfectly in line with Huygens’s principle, with prediction that every point in an electromagnetic wave would act as a source of the continuing wave.
USES OF HUYGEN’S PRINCIPLE
- It served as a fundamental explanation of the wave nature of the light interference.
- Diffraction of light (the phenomenon of bending of wave around an obstacle or around the edges of an opening) can be easily explained using Huygen’s Principle.
- It explains the principle of reflection.
- It can be used to explain the phenomenon of refraction and interference.
- It is a useful technique to determine how and where the waves propagate.
- It helps in explaining the linear and spherical wave propagation.
LIMITATIONS OF HUYGEN’S PRINCIPLE
- It is a consequence of the homogeneity of space (the space is said to be uniform in all the locations).
- It was noticed by Jacques Hadamard in 1900, that Huygen’s principle could not be applied when the number of spatial dimensions was equal.