Huygens' Wave Theory, its merits and demerits

What is Huygens' Wave Theory, what are its assumptions 

let us see that in details 

👉Light emitted by a source propagates in the form of waves.

👉Huygens' original theory assumed them to be longitudinal waves.

👉In a homogeneous isotropic medium light from a point source

spreads by spherical waves.

👉It was thought that a wave  motion needed a medium for its propagation. Hence  the theory postulated a medium called luminiferous ether that  exists everywhere, in vacuum as well as in transparent bodies.

👉Ether had to be assigned some extraordinary properties, a high modulus of elasticity to account for the high speed of light, zero density so that it offers no resistance to planetary motions and perfect transparency.

👉The different colours of the light are due to the different wavelengths.

Merits

👉 Huygens' wave theory satisfactorily explains reflection and refraction.

👉In explaining refraction, the theory concludes that the speed of light in a denser medium is less than that in a rarer medium, which agreed with later experimental findings.

👉The theory was later used by Young (1800-04), Fraunhofer and Fresnel (1814) to satisfactorily explain interference, diffraction and rectilinear propagation of light.

Demerits

👉 It was found much later that the hypothetical medium , lumniferous ether has no experimental basis. In 1905 Einstien discarded the idea of ether completely.

👉Phenomena like absorption and emission of light by atoms and

molecules, photoelectric effect, Raman effect, Compton effect, etc., cannot

be explained on the basis of the wave theory.