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 hydrogen-inflated polythene balloon is released from the surface of the earth. As the balloon rises to an altitude up in the atmosphere, what will happen to its shape and size? (UPSC Prelims 2003)
[A] Decrease in size
[B] Flatten into a disc-like shape
[C] Increase in size
[D] maintain the same size and shape
Show Answer
Correct Answer: C [Increase in size]
Notes:
As a weather balloon rises into high altitudes, where air pressure decreases, the helium or hydrogen pressure inside the balloon increases and expands the balloon. This way the balloon and the radiosonde can rise at a consistent pace high into the atmosphere.
32. An oil tanker is partially filled with oil and moves forward on a level road with uniform acceleration, How the free surface of oil behaves? (UPSC Prelims 2003)
[A] Remains horizontal
[B] It inclined to the horizontal with smaller depth at the rear end
[C] It inclined to the horizontal with larger depth at the rear end
[D] Assumes parabolic curve
Show Answer
Correct Answer: C [It inclined to the horizontal with larger depth at the rear end]
Notes:
The surface of tanker will move in forward direction with increasing velocity (as acceleration in uniform), so depth will be larger at the rear end.
33. Which among the following methods is used in the nuclear power reactors to produce energy for peaceful purpose?
[A] Nuclear fusion
[B] Nuclear fission
[C] Radioactive decay
[D] None of the above
Show Answer
Correct Answer: B [Nuclear fission]
Notes:
Nuclear energy can be harnessed by two methods namely nuclear fusion and nuclear fission. Nuclear fission involves breaking of a large nucleus into two or more nuclei where as nuclear fusion is the process of fusing (merging) two lighter nuclei. Fusion reaction releases enormous amount of energy (under high temperature and pressure) and is uncontrollable and hence it is not preferred in nuclear reactors.
Note: Nuclear fusion powers Sun and all the stars.
Extra info: Hydrogen bomb uses the process of nuclear fusion and hence it is the most powerful bomb.
34. Which among the following is not a vector quantity?
[A] Speed
[B] Velocity
[C] Acceleration
[D] Displacement
Show Answer
Correct Answer: A [Speed]
Notes:
Vectors are quantities which have both magnitude and direction where as scalars have only magnitude but not direction. Displacement, velocity, acceleration are vectors where as distance, speed are scalars.
35. 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.
36. The absolute zero is a temperature at which__?
[A] molecular motion in a gas would cease
[B] water freezes
[C] all gases become liquid
[D] all gases become solid
Show Answer
Correct Answer: A [molecular motion in a gas would cease]
Notes:
Absolute zero is the lowest possible temperature at which all atomic or molecular motion in matter stops. By international agreement, absolute zero is defined as precisely; 0 K on the Kelvin scale, which is a thermodynamic (absolute) temperature scale; and .273.15 degrees Celsius on the Celsius scale.
37. Newton-meter (Nm) is the SI unit of which of the following physical quantity?
[A] Acceleration
[B] Torque
[C] Power
[D] Force
Show Answer
Correct Answer: B [Torque]
Notes:
Newton metre (Nm) is the SI unit for torque. Torque, also known as moment, or moment of force, is a rotational force that can be thought of as a twist to an object. It is a measure of how much a force acting on an object causes that object to rotate.
38. The rate of change of displacement with time is known as__:
[A] Force
[B] Acceleration
[C] Retardation
[D] Velocity
Show Answer
Correct Answer: D [Velocity]
Notes:
The rate of change of displacement of an object (displacement over elapsed time) is velocity. Velocity is a vector since it has both magnitude (called speed) and direction.
39. Decibel is the unit used for__:
[A] Speed of light
[B] Intensity of heat
[C] Intensity of sound
[D] Radio wave frequency
Show Answer
Correct Answer: C [Intensity of sound]
Notes:
The decibel (abbreviated dB) is the unit used to measure the intensity of a sound. The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities. The decibel is used for a wide variety of measurements in science and engineering, most prominently in acoustics, electronics, and control theory.
40. A spherical ball made of steel when dropped in mercury container__:
[A] It will sink in mercury
[B] It will be on the surface of mercury
[C] It will be partly immersed mercury
[D] It will dissolve in mercury
Show Answer
Correct Answer: B [It will be on the surface of mercury]
Notes:
The density of steel usually ranges between 7.75 and 8.05 g/cm3 and the density of mercury is 13.534 g/cm3. Mercury is denser than steel therefore the buoyant force is large enough to force float the steel ball.
