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 material is commonly used to make control rods in a nuclear reactor?
[A] Indium
[B] Boron
[C] Cadmium
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
Control rods are made of boron, silver, indium and cadmium that are capable of absorbing many neutrons without themselves fissioning.
32. What is the value of Rydberg constant?
[A] 1.0973 x 103 m-1
[B] 1.0973 x 105 m-1
[C] 1.0973 x 107 m-1
[D] 1.0973 x 109 m-1
Show Answer
Correct Answer: C [1.0973 x 107 m-1]
Notes:
The value of Rydberg constant is 1.0973 x 107 m-1
33. What happens to the resistance of a p-n junction diode when forward biased?
[A] it becomes high
[B] No effect
[C] it becomes low
[D] it becomes zero
Show Answer
Correct Answer: C [it becomes low]
Notes:
The resistance of a p-n junction diode becomes low when forward biased and becomes high when reverse biased. This is the principle of the working of rectifier.
34. 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.
35. At what condition a body partially floats in water?
[A] The volume of the displaced liquid is equal to the volume of the body
[B] The volume of the displaced liquid is greater than the volume of the body
[C] The weight of the displaced water is equal to the weight of the body
[D] The weight of the displaced water is greater than the weight of the body
Show Answer
Correct Answer: C [The weight of the displaced water is equal to the weight of the body]
Notes:
All the objects placed in a liquid experience an upward force which allows the body to float if it displaces water with the weight equal to the weight of the body. This upward force is known as buoyant force and the law is known as the law of buoyancy. Mainly, floatation depends upon the density.
36. Which of the following techniques is used to transmit audio signals in television broadcasts?
[A] Amplitude Modulation
[B] Frequency Modulation
[C] Pulse Code Modulation
[D] Time Division Multiplexing
Show Answer
Correct Answer: B [Frequency Modulation]
Notes:
Frequency modulation is a process in which the frequency of the carrier is varied in accordance with the instantaneous value of modulating voltage. In telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. FM is most commonly used for radio and television broadcasting.
37. Which one of the following layers of the atmosphere is responsible for the deflection of radio waves?
[A] Troposphere
[B] Stratosphere
[C] Mesosphere
[D] Ionosphere
Show Answer
Correct Answer: D [Ionosphere]
Notes:
The layer of the atmosphere that reflects radio waves is the ionosphere. That is because there are gas particles in the ionosphere that are ionized.
38. 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?
[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.
39. 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.
40. What will be the weight of a body at the centre of earth?
[A] half the weight at the surface
[B] zero
[C] twice the weight at the surface
[D] infinite
Show Answer
Correct Answer: B [zero]
Notes:
Weight of a body is the force with which it is attracted towards the centre of earth. The weight of a body, ‘W’ of mass ‘m’ is given by: W = mg, where ‘g’ is the acceleration due to gravity. At the centre of earth, value of ‘g’ is zero. Therefore, weight of a body will be zero at the centre of the earth.
