Optics (Physics) Part-I

Total Questions: 50

21. Which of the following does not change when light travels from one medium to another? [66ᵗʰ B.P.S.C. (Pre) 2020]

Correct Answer: (c) Frequency
Solution:

When light travels from one medium to another, the frequency of the light does not change, while its velocity, wavelength and refractive index of the medium are changed.

22. When light waves pass from air to glass the variable affected are- [I.A.S. (Pre) 2001]

Correct Answer: (d) Wavelength and velocity
Solution:

When light travels from one medium to another, the frequency of the light does not change, while its velocity, wavelength and refractive index of the medium are changed.

23. When light passes from one medium to another medium, which one of the followings does not change : [U.P.P.C.S. (Mains) 2003]

Correct Answer: (d) Frequency
Solution:

When light travels from one medium to another, the frequency of the light does not change, while its velocity, wavelength and refractive index of the medium are changed.

24. When a ray of light travels from a denser medium to a rarer medium then. [Chattisgarh P.C.S. (Pre) 2018]

Correct Answer: (a) It speeds up and bends away from the normal
Solution:

When a ray of light travels from a denser medium to a rarer medium it speeds up and bends away from the normal. If ray of light travels from a rarer to a denser medium, it slows down and bends towards the normal in the denser medium.

25. The formation of glittering colours in thin foam of soap is the result of which of the following phenomenon- [I.A.S. (Pre) 1993]

Correct Answer: (a) Total reflection and interference
Solution:

The formation of glittering colour in thin foam of soap is the result of the phenomenon of total reflection and interference. When light waves hit a bubble, some of them bounce straight back off the outer part of the soap film.

Others refracted on through but then bounce off the inner part of the film. Now refracted and reflected light gives soap foam glittering colour.

26. Total internal reflection can take place when light travels from: [I.A.S. (Pre) 1996]

Correct Answer: (a) Diamond to glass
Solution:

Total internal reflection takes place when a ray of light is travelling from denser to rarer medium and angle of incidence is greater than the critical angle, the ray is completely reflected from the surface.

So according to options, the situation of option (a) is correct where total internal reflection takes place, it is because diamond is denser than glass.

27. A cut diamond shines brilliantly due to [U.P.P.C.S. (Pre) 2017, U.P.P.C.S. (Mains) 2015]

Correct Answer: (b) Total internal reflection
Solution:

A cut diamond shines brilliantly due to total internal reflection of light. Diamond shines more than a glass piece because of its low critical angle 24.4 degrees. This is the reason why diamond shines more than a glass piece of same shape.

28. The diamond appears lustrous because of: [U.P.P.C.S. (Mains) 2012, U.P.P.C.S. (Pre) 1996]

Correct Answer: (c) Total Internal Reflection
Solution:

The refractive index of diamond is very high and therefore its critical angle is very low. Diamond achieves brilliance from total internal refraction.

It has been cut or designed in such a way that if light enters in-to it, incident light strikes many of the internal surfaces. After many such total internal reflections, the colours in the light are separated and hence seen individually.

29. What is the reason behind the extra ordinary shining of the diamond cuts in a proper way? [I.A.S. (Pre) 1994]

Correct Answer: (b) Because it has a higher refractive index
Solution:

The refractive index of diamond is very high and therefore its critical angle is very low. Diamond achieves brilliance from total internal refraction.

It has been cut or designed in such a way that if light enters in-to it, incident light strikes many of the internal surfaces. After many such total internal reflections, the colours in the light are separated and hence seen individually.

30. Given below are two statements, one labeled as Assertion (A) and other labeled as Reason (R): [I.A.S. (Pre) 1995]

Assertion (A): A diamond sparkles more than a glass imitation cut to the same shape.

Reason (R): The refractive index of diamond is less than that of glass.

In the context of the above two statements, which one of the following is correct?

Correct Answer: (c) A is true but R is false.
Solution:

A diamond sparkles more than a glass crystal of the same shape and size, because the refractive index of diamond is very high (μ = 2.42). Therefore its critical angle get reduced which results in less opportunity for light to exit.

So the light reflects off the diamond's inner surfaces several times before it finally exits. The refractive index of glass is 1.51. Thus, statement A is true but reason R is false.