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Explain how 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 the experiment?

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Suppose that the light corpuscles traveling with a velocity C in rarer medium along A O strike the interface X Y separating the denser medium (say, water) from a rarer medium as shown in above figure. After refraction, the light corpuscles travel inside he denser medium along O B with a velocity V. Let i and r be the angles of incidence and reflection respectively.

According to Newton’s corpuscular theory, the light corpuscles experience a force of attraction due to the denser medium, which acts along normal to the interface X Y. Obviously, the component of their velocities before and after the refraction along X Y must remain the same.

i.e., velocity of the light corpuscles in a denser medium is greater than that in a rarer medium. This result of the corpuscular theory is against the experimental result and therefore this theory was discarded. On the basis of Huygen’s wave theory, the phenomenon of refraction can be easily explained and it can be proved that c > v. Therefore, wave picture of light is consistent with experimental result.

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