Question

A ray of light passes from an optically rarer medium A to an optically denser medium B.No refraction of light occurs if the angle of incidence in the optically rarer medium is: (a) 120° (b) 90° (c)45° (d) 0°​

Answer 1

Correct option is

C

π−2C

Given: A ray of light travels from an optically denser to rarer medium. The critical angle for the two media is C.

To find the maximum possible deviation of the ray

Solution:

Critical angle is the angle of incidence for which the angle of refraction is

2

π

for a given pair of media.

Let θ be the angle of incidence and ϕ the angle of refraction.

When the ray passes from denser to rarer medium, the deviation is δ=ϕ−θ. If θ=C then ϕ=

2

π

and deviation δ=

2

π

−C. This is the maximum deviation. When total internal reflection occurs, the deviation is given by δ=π−2θ. Here δ is maximum when θ is minimum. The minimum value of θ is C.

Hence maximum deviation δ=π−2C.

Hope this will help you

Answer 2

No refraction of light occurs if the angle of incidence in the optically rarer medium is (d) $0^{o}$.

Explanation:

• Refraction is a particle property of light.
• Whenever light travels through mediums of different densities, the ray of light tends to bend towards or away from normal.
• A normal is a perpendicular line on the interface of two mediums.
• The angle of incidence is the angle made by incident ray with the normal.
• Light travels faster in rarer medium and slower in denser medium.
• Refracted ray bends away or towards the normal depending on the density of second medium in relative to the density of first medium.
• When light ray travels from denser medium to rarer medium, speed of light increases and the refracted ray bends away from normal.
• When light ray travels from rarer medium to denser medium, speed of light decreases and the refracted ray bends towards normal.

When light ray is incident with an angle of $0^{0}$, which means when light ray is along the normal, then there is no refraction and the angle of refraction is $0^{0}$.