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. A corked bottle full of water when frozen will break due to which of the following reasons? (UPSC Prelims 1994)
[A] the bottle contracts on freezing
[B] the volume of water decreases on freezing
[C] the volume of water increases on freezing
[D] glass is a bad conductor of heat
Show Answer
Correct Answer: C [the volume of water increases on freezing]
Notes:
If you put a glass bottle in the freezer, the level of the liquid will decrease as the temperature drops, until 3.98 C, at which point it starts to expand again as the volume of water increases on freezing. So unless the glass jar is tremendously strong, as the water freezes, it will break.
32. 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.
33. In which among the following mediums, the speed of sound is maximum?
[A] Vacuum
[B] Air
[C] Water
[D] Steel
Show Answer
Correct Answer: D [Steel]
Notes:
Sound being a longitudinal wave, its speed is directly proportional to the density of the medium. The denser the medium, the faster is the sound. Among the given options, density is more in steel and hence the speed of sound is more in steel compared to other three.
Extra info: Speed of sound in steel : 5960 mts/second.
Speed of sound in air: 330 mts/second.
Speed of sound in vacuum: 0 mts/second.
34. What is an object which is so massive that light cannot escape its gravity called?
[A] Supernova
[B] Pulsar
[C] Black Hole
[D] Quasar
Show Answer
Correct Answer: C [Black Hole]
Notes:
Black hole is an object that is so massive that light cannot escape its gravity. Astronomers can detect black holes by using X-ray telescopes.
35. Which of the following pairs of physical quantities have the same dimensions?
[A] Force and Power
[B] Work and Power
[C] Work and Energy
[D] Momentum and Power
Show Answer
Correct Answer: C [Work and Energy]
Notes:
The term energy is used to describe the capacity of a system to do work on another system. Energy of all types (Surface tension, Kinetic, Potential etc.) have the same dimension and unit as that of work with same dimensional formula of M1L2T-2. In the SI system, both have the same units of Newton meter.
36. 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.
37. A body moving in a circular path with a constant speed has a
[A] constant velocity
[B] constant acceleration
[C] constant kinetic energy
[D] constant displacement
Show Answer
Correct Answer: C [constant kinetic energy]
Notes:
In circular motion, the magnitude of the velocity of the body is constant but the direction is constantly changing. This means that, even though the speed is not changing, the velocity is changing. This means that body moving in a circular is accelerating. A body moving at constant speed in a circular path experiences an acceleration directed towards the centre of the circular path. Thus, kinetic energy remains constant because the speed is constant.
38. Measurement means the comparison of an unknown quantity with some known fixed quantity called a ______.
[A] Unit
[B] Scale
[C] Order
[D] Standard
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Correct Answer: A [Unit]
Notes:
Measurement means the comparison of an unknown quantity with some known or fixed quantity of same kind. This known or fixed quantity is called a unit. This unit is used as a standard unit of measurement. For taking any measurement, we need a unit and then we find out how many times, the unit is contained in the given quantity.
39. Which of the following is the SI unit of temperature?
[A] Kelvin
[B] Reaumur scale
[C] Candla
[D] Ampere
Show Answer
Correct Answer: A [Kelvin]
Notes:
SI unit of temperature is Kelvin. The Kelvin (K) is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The temperature 0 K is commonly referred to as “absolute zero”.
40. Oil rises up the wick in a lamp because__:
[A] Oil is very light
[B] Of the di ffusion of oi l through the wick
[C] Of the surface tension phenomenon
[D] Of the capillary action phenomenon
Show Answer
Correct Answer: D [Of the capillary action phenomenon]
Notes:
It is because of the capillary action that oil rise up the wick in a lamp. Capillary action, or capillarity, is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper.
