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.
21. In which of the following cases Doppler effect is not seen?
[A] When the velocity of source and listener is equal to or greater than the sound velocity
[B] When source and listener moves in opposite direction
[C] When the velocity of source and listener is less than the sound velocity
[D] None of the above
Show Answer
Correct Answer: A [When the velocity of source and listener is equal to or greater than the sound velocity]
Notes:
If the velocity of source and listener is equal to or greater than the sound velocity then Doppler effect is not seen.
22. Which of the following is correct about the speed of the sound, at same temperature?
[A] sound travels faster in humid air than in dry air
[B] sound travels slower in humid air than in dry air
[C] speed of sound is same in humid air and dry air
[D] None of the above
Show Answer
Correct Answer: A [sound travels faster in humid air than in dry air]
Notes:
With increase in humidity, density of air decreases. So with rise in humidity velocity of sound increases. This is why sound travels faster in humid air (rainy season) than in dry air (summer) at the same temperature.
23. What do we call the temperature at which the liquid and the vapour states of the substance coexist?
[A] Freezing point
[B] Melting point
[C] Boiling point
[D] Normal point
Show Answer
Correct Answer: C [Boiling point]
Notes:
The temperature at which the liquid and the vapour states of the substance coexist is called its boiling point.
24. Which of the following is correct about Convection?
[A] It is possible in solids only
[B] It is possible in fluids only
[C] It is possible in solids and gases only
[D] None of the above
Show Answer
Correct Answer: B [It is possible in fluids only]
Notes:
Convection is a mode of heat transfer by actual motion of matter. It is possible only in fluids.
25. Which of the following is true about the force between two point charges as per the Coulomb’s law?
[A] inversely as the square of the distance between the charges
[B] directly proportional to the product of the magnitude of the two charges
[C] Both a and b
[D] None of the above
Show Answer
Correct Answer: C [Both a and b ]
Notes:
As per Coulomb’s law, the force between two point charges varied inversely as the square of the distance between the charges and was directly proportional to the product of the magnitude of the two charges and acted along the line joining the two charges.
26. 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.
27. What is the output of an OR gate when both the inputs are 1?
[A] 0
[B] 1
[C] Either 0 or 1
[D] None
Show Answer
Correct Answer: B [1]
Notes:
The OR gate is a digital logic gate that gives a HIGH output if one or both the inputs to the gate are HIGH.
28. What are the majority charge carriers in p-type semiconductors?
[A] electrons
[B] holes
[C] equal concentration of holes and electrons
[D] None of the above
Show Answer
Correct Answer: B [holes]
Notes:
Note that in a p-type semiconductor, more holes are created due to addition of acceptor impurity than by breaking covalent bonds due to thermal energy at room temperature. Hence, the net concentration of holes is significantly greater than that of electrons. That is, in a p-type semiconductor, the holes are the majority charge carriers.
29. “Mach Number” is a term associated with the speed of which of the following?
[A] Ships
[B] Cars
[C] Aeroplanes
[D] Light
Show Answer
Correct Answer: C [Aeroplanes]
Notes:
Mach number is a measure of speed of an aeroplane. When we say an aircraft is flying at Mach 1, it means that the speed of the vehicle is 343 m/s. Mach number is the ratio between the true airspeed of the aircraft and the local speed of sound.
30. 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.
