According to Huygens principle,the phase difference between oscillations of any two particles on the same wave front is . . . . . . rad.

$A$ point source of light is placed at the focus of a concave mirror. Consider only paraxial rays. The shapes of the wavefronts of incident and reflected lights respectively are

The main drawback of Huygens' theory was:

Explain how the Corpuscular theory predicts the speed of light in a medium,such as water,to be greater than the speed of light in a vacuum. Is this prediction confirmed by the experimental determination of the speed of light in water? If not,which alternative picture of light is consistent with the experiment?

Which of the following is correct for light diverging from a point source?

For light diverging from a finite point source,