Answer:
Let the second medium be air (n₁=1)
The refractive index n₂ of the medium where first medium is air is found (a)
(a) n₂ = 2
Explanation:
Critical angle can be defined as the angle of incidence that provides the angle of refraction of 90°.
Refractive index of a medium can be defined as a number that describes that how fast a light will travel through that medium.
Critical angle and Refractive index are related by:


To find refractive index of medium with respect to air, substitute n₁=1 (Refractive index of air is 1)
Also θ(critical)=30°
Find n₂ :

Yes it is valid all the times under the consideration of acceleration due to gravity .it is not valid on space where there is no influence of gravity
Photon is a quantum of light or a single packet/particle of light at a given wavelength.
Answer: Option B
<u>Explanation:
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It is known that light has dual nature of wave as well as particles. Light waves can behave in wave nature as well as in particle nature depending upon the situation. So the light waves are assumed in different views to easily understand the nature of light waves.
There are several models proposed to simplify the nature of light. Among the several assumptions, one of the most prominent observations are that light waves or quantum of light are termed as photons which are made up of single packet/particles of light in a given wavelength.