The speed of light in water is less than the speed of light in air,confirms the assumption of which theory of light?

You have learnt in the text how Huygens' principle leads to the laws of reflection and refraction. Use the same principle to deduce directly that a point object placed in front of a plane mirror produces a virtual image whose distance from the mirror is equal to the object distance from the mirror.

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

What is visible light? Write various views on it.

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.

Mention the main difficulty in establishing the wave theory of light.