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

Explain the use of wavefront to understand wave propagation.

Assertion $A$: For light diverging from a point source,the intensity at the wavefront does not depend on the distance.
Reason $R$: In a diverging beam of light from a point source,a spherical wavefront is observed.

State and explain Huygens' principle.

In the adjoining diagram, a wavefront $AB$ moving in air is incident on a plane glass surface $XY$. Its position $CD$ after refraction through a glass slab is shown along with the normals drawn at $A$ and $D$. The refractive index of glass with respect to air $(\mu = 1)$ will be equal to

What is the most important point of Huygens' wave theory?