Question

A crack in a glass vessel often shines like a mirror because of:
A) Total reflecting surface
B) Reflection
C) Refraction
D) All

Answer 1

Hint:A phenomenon in which the rays of light travel from a denser medium to a rarer medium is known as total internal reflection. This phenomenon occurs when there are two mediums. In this problem, this concept will be used.

Complete step-by-step answer:
Step I:
When a ray of light enters from a denser medium to a rarer medium, the angle of incidence should be greater than the critical angle. The critical angle in total internal reflection is the angle of incidence, at which the angle of refraction is ${90}^{\circ }$ .

Step II:
Given that there is a crack in the glass vessel, so two mediums will be there. One medium is glass and the other medium is air. This is because the air rushes in, from the crack in the vessel. Since glass is more denser than the air, so the light rays travelling from glass to air will suffer total internal reflection at the critical angle.
Step III:
In case when the two mediums are glass and air, when the angle of incidence is greater than ${42}^{\circ }$ , the critical angle is formed. Therefore the glass vessel will shine.

Therefore, option A is the right answer.

Note:The critical angle is basically the angle of incidence beyond which the rays of light passing from a denser medium to a rarer medium will not refract. They will completely suffer reflection instead of refraction. The value of critical angle can be calculated using Snell’s law. While using Snell’s law, the value of angle of refraction should be ${90}^{\circ }$ .