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. At which of the following speeds radio waves travel?
[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.
32. The alpha-particle carries two positive charges. Its mass is very nearly equal to that of?
[A] two protons
[B] an atom of helium
[C] sum of masses of two positrons and two neutrons
[D] two positrons as each positron carries a single positive charge
Show Answer
Correct Answer: B [an atom of helium]
Notes:
Each alpha particle contains two protons and two neutrons. Total number of nucleons = Number of protons + Number of neutrons = 2 + 2 = 4 Total number of nucleons = Mass number of an element Thus mass number of alpha particle is 4 which is equal to molecular weight of helium atom.
33. Which one of the following is the correct sequence of the given substances in the decreasing order of their densities?
[A] Steel>Mercury>Gold
[B] Gold>Mercury>Steel
[C] Steel>Gold>Mercury
[D] Gold>Steel>Mercury
Show Answer
Correct Answer: B [Gold>Mercury>Steel]
Notes:
Density of gold is 19.30 g/cm3.
The density of ultra pure liquid mercury is 13.534 g/cm3
The density of steel is 7.80 g/cm3.
34. One bar is equal to how many pascals?
[A] 103 Pa
[B] 100 Pa
[C] 105 Pa
[D] 104 Pa
Show Answer
Correct Answer: C [105 Pa]
Notes:
The bar is a non-SI unit of pressure. It is defined by the IUPAC as exactly equal to 100,000 Pa or 105Pa.
35. The density of water is 1 g/cc at__:
[A] 0°C
[B] 4°C
[C] 25°C
[D] 100°C
Show Answer
Correct Answer: B [4°C]
Notes:
Water has its maximum density of 1g/cm3 at 4 degrees Celsius. When the temperature changes becoming either greater or less than 4 degrees, the density also changes with change in volume.
36. Which of the following is the SI unit of luminous emittance?
[A] Lux
[B] Candela
[C] Lumen
[D] Lumen second
Show Answer
Correct Answer: A [Lux]
Notes:
The lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square metre. In photometry, it is used as a measure of the intensity, as perceived by the human eye of light that hits or passes through a surface.
37. What does the slope of a Distance-Time graph show?
[A] acceleration
[B] momentum
[C] mass
[D] speed
Show Answer
Correct Answer: D [speed]
Notes:
Distance-time graph is the plot of distance travelled by a body against time. Distance is plotted on the Y-axis (left) and Time is plotted on the X-axis (bottom). The slope of the graph indicates the speed of the object. ‘Straight lines’ on a distance-time graph tell us that the object is travelling at a constant speed.
38. Why we feel cool when we sit near the fan?
[A] fan gives cool air.
[B] fan cools surrounding air.
[C] air vapourises the sweat on our body.
[D] we feel cool when air touches the body.
Show Answer
Correct Answer: C [air vapourises the sweat on our body.]
Notes:
We feel comfortable sitting under a fan when we are perspiring because a fan increases the rate of evaporation of sweat (or moisture) from our body and makes us feel cool and comfortable. Evaporation of water has cooling effect. Fanning also help remove the hot/warm air away form body surface quickly.
39. The average kinetic energy of the molecules of an ideal gas is directly proportional to__:
[A] Velocity of Molecules
[B] Mass of Molecules
[C] Absolute temperature of the gas
[D] Temperature of environment
Show Answer
Correct Answer: C [Absolute temperature of the gas]
Notes:
The average kinetic energy of gas molecules is directly proportional to absolute temperature only. This implies that all molecular motion ceases if the temperature is reduced to absolute zero.
40. Which of the following is the unit of perceived loudness of sound ?
[A] Decibel
[B] Sone
[C] Hertz
[D] Phon
Show Answer
Correct Answer: B [Sone]
Notes:
Perceived loudness of sound is a psycho-acoustic quantity that depends on sound pressure level, the frequency spectrum, and the time behavior of the sound. The sone is a unit of perceived loudness that was proposed by Stanley Smith Stevens in 1936.Being a unit of how loud a sound is perceived, the sone scale of loudness is based on data obtained from subjects who were asked to judge the loudness of pure tones and noise. One sone is arbitrarily set equal to the loudness of a 1,000-hertz tone at a sound level of 40 decibels.
