When wavefronts pass from a denser medium to a rarer medium, the width of the wavefront

Derive the laws of refraction using the concept of Huygens' principle of wavefronts.

Explain how to obtain a new wavefront at time $\tau$ using Huygens' principle for a plane wavefront.

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?

The phase difference between any two particles in a given wavefront is . . . . . . rad.

$A$ light wave is propagating with plane wave fronts of the type $x+y+z=$ constant. The angle made by the direction of wave propagation with the $x$-axis is