Physics MCQs
Physics Objective (Multiple Choice) General Knowledge & General Science Questions & Answers for SSC-CGL, UPPSC, NDA, CDS and all one day examinations of India.
31. Why does a black board appear black in colour?
[A] It reflects all colours
[B] It absorbs black colour
[C] It absorbs all the colours
[D] It reflects black colour
Show Answer
Correct Answer: C [It absorbs all the colours]
Notes:
Actually a black board has all colours in light or white light . So when light falls on it board absorbs all colours because all are present so no light is reflected back . That is the case when board has all colours and so it will appear black as it absorbs all colours of light that fall on it .
32. Which of the following situations arises when a man circles round the earth in a satellite?
[A] The mass of man becomes zero but weight remains constant
[B] The Mass of man remains constant but weight becomes zero
[C] Both mass and weight of the man remain constant
[D] Both mass and weight of the man remain zero
Show Answer
Correct Answer: B [The Mass of man remains constant but weight becomes zero]
Notes:
Mass is the amount of matter enclosed by a body so it can never change with displacement in a body. Weight is a force actually force due to gravity taking earth into consideration. Therefore outside earth this force is negligible. Hence weight is zero. As W=mg, where g is the force due to gravity. When ‘g’ is almost negligible or nil, weight becomes zero. Hence outside earth weight is zero while mass is constant.
33. The surface of the water in a lake is frozen and its temperature is -15°C. Which of the following will be the maximum possible temperature of the water inside the lake in contact with the ice layer? (UPSC Prelims 1984)
[A] 0°C
[B] 4°C
[C] 15°C
[D] Insufficient data to predict
Show Answer
Correct Answer: B [4°C]
Notes:
During winter ice is formed only on the top layer of a pond or a lake because the water’s surface is usually slightly cooler than the rest of the body of water due to evaporative cooling. As water cools below 4 C, it also becomes slightly less dense, rising to the surface. Ice is also slightly less dense than the slightly warmer water below, so it floats on the water’s surface. Once ice crystals begin to form, they provide nucleation sites for additional ice to grow along the water’s surface. The islands of ice expand, until they cover the entire surface of the water.
34. At which of the following speeds radio waves travel? (UPSC Prelims 1985)
[A] 3 x 106 m/sec
[B] 3 x 107 m/sec
[C] 3 x 108 m/sec
[D] 3 x 109 m/sec
Show Answer
Correct Answer: C [3 x 108 m/sec]
Notes:
Radio waves travel very quickly through space. Radio waves are a kind of electromagnetic radiation, and thus they move at the speed of light. The speed of light is a little less than 300,000 km per second. At that speed, a beam of light could go around the Earth at the equator more than 7 times in a second.
35. Which of the following is the normal temperature of human body on the Kelvin scale? (UPSC Prelims 1995)
[A] 280
[B] 290
[C] 300
[D] 310
Show Answer
Correct Answer: D [310]
Notes:
Normal body temperature of human is 37° C. But when we convert 37° C into Kelvin it becomes 310 K because 0° C = 0°C + 273 = 273 K.
36. When light waves pass from air to glass, which of the following variables are affected? (UPSC Prelims 2001)
[A] Wavelength, frequency and velocity
[B] Velocity and frequency
[C] Wavelength and frequency
[D] Wavelength and velocity
Show Answer
Correct Answer: D [Wavelength and velocity]
Notes:
When light enters from rarer (air) to denser (glass) medium wavelength and velocity will get affected. The velocity will decrease. Moreover, as the ray bent in passing through different media which results in decrease of wavelength. As such there is no change in frequency when light enters from air to glass.
37. Which type of wave is sound wave?
[A] Transverse wave
[B] Longitudinal wave
[C] Electromagnetic wave
[D] None of the above.
Show Answer
Correct Answer: B [Longitudinal wave]
Notes:
Sound is a longitudinal wave. Longitudinal wave is a wave where the direction of propagation of the wave and movement of particles is in the same direction where as in transverse wave they are perpendicular to each other.
Extra info: Example of transverse wave is light wave (electromagnetic wave).
38. When a body falls from an aeroplane, there is increase in its__:
[A] Kinetic energy
[B] Mass
[C] Acceleration
[D] Potential energy
Show Answer
Correct Answer: C [Acceleration]
Notes:
The energy possessed by a body by virtue of its motion is called kinetic energy. Potential Energy is the energy possessed by virtue of its position or configuration. When a body falls from an aeroplane, there is increase in its acceleration as it fall under the influence of force of gravity.
39. To open a door easily, the handle is fixed at farthest point from hinges. This is mainly because at greater distance from hinges, there is more __:
[A] Force
[B] Torque
[C] Load
[D] Thrust
Show Answer
Correct Answer: B [Torque ]
Notes:
Since Torque = force x distance, to open a door easily, the handle should be fixed at the greatest distance from the hinges. If we pull with same force on a handle that is 2 feet away from the hinges, we will provide twice the torque, so it will be twice as easy to open.
40. What happens to the density of water when it freezes?
[A] Decreases
[B] Becomes Zero
[C] Remains constant
[D] Increases
Show Answer
Correct Answer: A [Decreases]
Notes:
Water at ordinary temperatures contracts and increases in density as it is cooled, like most substances. But at 4°C, it reaches its maximum density and then decreases in density as it approaches the freezing point. This is referred to as anomalous property of water according to which density reduced with the decreasing temperature.