UPSC  Physics

91. Cloudy nights are warmer compared to clear cloudless nights, because clouds:

prevent clod waves from the sky from descending on earth reflect back the heat given off by earth produce heat and radiate it towards earth absorb heat from the atmosphere and send it towards earth

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92. Given below are two statements
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 context of the above two statements, which one of the following is correct?

Both A and R are true and R is the correct explanation of A Both A and R are true and R is not a correct explanation of A A is true but R is false A is false but R is true

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93. Suppose a rocketship is receding from the earth at a speed of 2/10 th the velocity of light. A light in the rocketship appears blue to the passengers on the ship. What colour would it appear to an observer on the earth?

Blue Orange Yellow Yellow-orange

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94. Match List I (Quantity) with List II (Units) and select the correct answer using the codes given below the lists:
List-I List-II
A. High speed 1. Mach
B. wavelength 2. Angstrom
C. Pressure 3. Pascal
D. energy 4. Joule
Codes:

A-2, B-1, C-3, D-4 A-1, B-2, C-4, D-3 A-1, B-2, C-3, D-4 A-2, B-1, C-4, D-3

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95. Consider the following statements:
1. If a person looks at a coin which is in a bucket of water, the coin will appear to be closer than it really is.
2. If a person under water looks at a coin above the water surface, the coin will appear to be at a higher level than it really is.
Which of the above statements is/are correct?

1 and 2 1 alone 2 alone neither 1 nor 2

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96. When a CD (compact disc used in audio and video systems) is seen in sunlight, rainbow like colours are seen. This can be explained on the basis of the phenomenon of:

reflection and diffraction reflection and transmission diffraction and transmission refraction, diffraction and transmission

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97. Assertion (A): A stick is dipped in water in a slanting position. If observed sideways, the stick appears short and bent at the surface of water.
Reason (R): A light coming from the stick undergoes scattering from water molecules giving the stick a short and bent appearance.

Both A and R are true and R is the correct explanation of A Both A and R are true but R is not a correct explanation of A A is true but R is false A is false but R is true

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98. Consider the following statements:
1. Light of longer wavelength are scattered much more than the light of shorter wavelength.
2. The speed of visible light in water is 0.95 times the speed in vacuum.
3. Radio waves are produced by rapidly oscillating electrical currents.
4. To detect the over speeding vehicles, police use the Doppler effect of reflected short radio waves.
Which of these statements are correct?

1 and 2 1 and 3 2 and 4 3 and 4

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99. Consider the following natural phenomena:
1. Terrestrial heating
2. Reflection of light
3. Refraction of light
4. Diffraction of light
Due to which of these phenomena is a mirage formed?

1 and 2 2, 3 and 4 1 and 3 4 only

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100. Which one of the following statements is not correct?

The velocity of sound in air increases with the increase of temperature The velocity of sound in air is independent of pressure The velocity of sound in air decreases as the humidity increases The velocity of sound in air is not affected by the change in amplitude and frequency

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