Mock Test

Optics part (1)

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Optics part (1)

Total Questions: 78

21. Which of the following does not change when the 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 remains constant, while its velocity, wavelength, and refractive index of the medium change.

22. When the light waves passes from the 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 remains constant, while its velocity, wavelength, and refractive index of the medium change.

23. When the light passes from the one medium to another medium which one of the following 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 remains constant, hence it not change. while its velocity, wavelength, and refractive index of the medium change.

24. When a ray of light travel a denser medium to rare medium then [Chhattisgarh 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 the a denser medium to a rarer medium it speeds up and bends away from the normal .If the ray of light travels from the 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 reflect off the front and back surfaces of the thin soap film, they interfere with each other.

reflection of light off of both the outer and inner surfaces of the thin film is a key part of the process that allows the light waves to interfere. Now refracted and reflected light gives soap foam glittering colour.

26. Total internal reflection can take place when light travels from: [LA.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 diamonds shines brilliantly due to [U.P.P.C.S.(MAINS) 2015, U.P.P.C.S.(pre) 2017]

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. A diamonds 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 reflection. It has been cut or designed in such a way that if light enters into it, the incident light strikes many of the internal surfaces.

After many such total internal reflections, the light is dispersed due to high dispersion of diamond, which causes the colours in the light to separate and hence be seen individually.

29. What is the reason behind the 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 reflection. It has been cut or designed in such a way that if light enters into it, the incident light strikes many of the internal surfaces.

After many such total internal reflections, the light is dispersed due to high dispersion of diamond, which causes the colours in the light to separate and hence be 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 (u=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.

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