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. Which of the following is a commonly used moderator in a Nuclear reactor?
[A] Heavy water
[B] Graphite
[C] Water
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
Commonly used moderators include water, graphite and heavy water.
32. Which of the following represents the angular momentum of an electron as per Bohr’s model (h= Planck’s constant)?
[A] h/π
[B] nh/2π
[C] 2πnh
[D] πnh
Show Answer
Correct Answer: B [nh/2π]
Notes:
Bohr’s postulate states that the electron revolves around the nucleus only in those orbits for which the angular momentum is some integral multiple of h/2π where h is the Planck’s constant (= 6.6 × 10–34 J s). Thus the angular momentum (L) of the orbiting electron is quantised. That is L = nh/2π
33. What is the barrier potential for Germanium?
[A] 0.3 V
[B] 0.7 V
[C] 1 V
[D] 1.7 V
Show Answer
Correct Answer: A [0.3 V]
Notes:
The barrier potential is characteristic of the semiconductor material. It is about 0.3 V for Germanium.
34. Which of the following devices is best suited for measuring the temperature inside metallurgical furnaces?
[A] Pyrometer
[B] Thermistor
[C] Thermocouple
[D] Thermometer
Show Answer
Correct Answer: A [Pyrometer]
Notes:
Pyrometer is a device for measuring relatively high temperatures, such as are encountered in furnaces. Most pyrometers work by measuring radiation from the body whose temperature is to be measured.
35. It is difficult to fix a nail on a freely suspended wooden frame. Which law supports this statement?
[A] Law of inertia
[B] Pascal’s law
[C] Newton’s third law
[D] Newton’s second law
Show Answer
Correct Answer: C [Newton’s third law]
Notes:
When the wooden block is not resting against a support, the block and nails both move forward on being hit with a hammer. However, when the block is held firmly against a support, and the nail is hit, an equal reaction of the support drives the nail into the block.
36. At what temperature (in degree celsius), the numerical values on Celsius and Fahrenheit scales become equal?
[A] 40
[B] -40
[C] 273
[D] -273
Show Answer
Correct Answer: B [-40]
Notes:
To find the temperature when both are equal, we use an old algebra trick and just set ºF = ºC and solve one of the equations. So the temperature when both the Celsius and Fahrenheit scales are the same is -40 degrees.
37. What will happen to the portion of ship under water, when it enters a sea from a river?
[A] It will increase
[B] It will decrease
[C] It will show no change
[D] it will increase and decrease alternately
Show Answer
Correct Answer: B [It will decrease]
Notes:
When the ship enters the sea, the water is no more the river fresh water but the saline sea water which is denser. As a result the weight of water displaced is now more than what it was previously when the ship was in river. The upthrust increases and the ship rise up.
38. 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?
[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.
39. The least penetrating power ray is ____:
[A] X-Ray
[B] Alpha-Ray
[C] Beta-Ray
[D] Gama-Ray
Show Answer
Correct Answer: B [Alpha-Ray]
Notes:
Alpha-rays have high ionizing power but it is difficult for them to penetrate matter thoroughly. This is because alpha particles are likely to ionize the first thing they come into contact with; thus, they hold a small range of penetrating power. Beta rays have intermediate; while, Gamma Rays and X-Rays have maximum penetrating power.
40. What will happen when a strong beam of light is passed through a colloidal solution?
[A] Light will be scattered
[B] Light will pass unchanged
[C] Light will be absorbed
[D] Light will be reflected
Show Answer
Correct Answer: A [Light will be scattered]
Notes:
When a strong beam of light is passed across a colloidal solution, it undergoes scattering caused by the suspended particles present in it. This effect of scattering of light incident on colloidal solution is called Tyndall effect.
