Question
Explain how Newton’s Corpuscular theory predicts the speed of light in a medium, say water, to be greater than the speed of light in vacuum. Is the prediction confirmed by experimental determination of the speed of light in water? If not, which alternative picture of light is consistent with experiment?
Solution
According to Newton's Corpuscular theory of light, when corpuscles of light strike the interface XY, separating a denser medium from a rarer medium, the component of their velocity along XY remains the same.
If v1 is velocity of light in rarer medium (air),
v2 is velocity of light in denser medium (water),
i is angle of incidence, and
r is angle of refraction then,
Component of v1 along XY = v1 sin i
Component of v2 along XY = v2 sin r
As,
Since,
i.e., light should travel faster in water than in air.
This prediction of Newton s theory is opposite to the experimental result.
Huygens wave theory predicts that v2 < v1, which is consistent with experimental conclusion.
