Question

Why was corpuscular theory of light discarded?

Answer 1

When the light ray travels from rarer to denser medium, then the refracted ray bends towards the normal and speed of light ray in denser medium is less than that of rarer medium. These are basically Snell law.

Complete step by step answer:
Corpuscular theory predicted that if the ray of light (refraction) bends towards the normal then the speed of the light would be greater in the second medium.

$NN' \to$Normal
$PQ \to$Interface of two media
$\angle i \to$Incident angle
$\angle r \to$Refracted angle
In the above figure in which refraction of light ray shown with medium$- 1$ [rarer] to medium$- 2$ [denser]. According to corpuscular theory, when the light ray refracts in denser medium so light ray bends towards the normal and speed of light ray in medium$- 2$ $\left[ {{v_2}} \right]$should be greater than that of medium$- 1$ $\left[ {{v_1}} \right]$i.e. ${v_2} > {v_1}........\left( i \right)$
After the corpuscular theory, in an experiment, Foucault proved that on refraction of light ray, it bends towards the second medium that means medium$- 2$ [denser] with respect to medium$- 1$ [rarer] then the speed of light will be lesser in the second medium [medium$- 2$] i.e.${v_2} < {v_1}........\left( {ii} \right)$
So, equation (i) [corpuscular theory] is contradictory to equation (ii) [Foucault experiment].
Further by Huygens’s theory of refraction of light wave and also by the shell’s law for refraction, the experiment of `Foucault’ found true that means ${v_2} < {v_1}$ thus the corpuscular theory did not satisfactorily explained refraction.

Note:
Remember that in a denser medium particles lie closer to each other so the light entry from rarer to denser medium on entering denser medium starts bending towards normal and due to collision speed also decreases in denser medium.