General Science - Physics MCQs
Physics Objective (Multiple Choice) General Knowledge & General Science Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examinations.
21. Consider the following statements with respect to the Thermionic emission:
1. It is caused by electrons or ions that break loose from the metal surface due to heat energy
2. A metal cannot emit thermions at all temperatures
Which among the above statements is / are correct ?
[A] Only 1
[B] Only 2
[C] Both 1 & 2
[D] Neither 1 nor 2
Show Answer
Correct Answer: C [ Both 1 & 2]
Notes:
The thermionic emission is cased by electrons or ions that break loose from the metal surface due to heat energy. The minimum heat energy required to make a metal emit an electron (thermion), from its surface is called threshold energy or work function. Electron volt (eV): It is the smallest unit of work and is generally used to measure threshold energy. It is defined as the amount of work done, when a charge of 1.6 × 10–19 coulombs (charge of one electron), moves through two points in an electric field, at a potential difference of one volt. 1 eV = 1.6 × 10–19 C × V = 1.6 × l0–19 J. The minimum temperature at which a particular material emits thermions from its surface on heating is called threshold temperature. A metal cannot emit thermions at all temperatures. The thermions are emitted by a metal only when its temperature is higher than the threshold temperature. (b) 1eV = 1.6 × l0–19 C × 1 V = 1.6 × l0–19 J
22. In which of the following respects, the ultra-violet radiations are similar to white light?
- Both obey the laws of reflection and refraction
- Both travel with same speed in vacuum
- Both are equally active chemically
- Both are scattered equally
Select the correct option from the codes given below:
[A] Only 1
[B] Only 1 & 2
[C] Only 1, 2 & 3
[D] 1, 2, 3 & 4
Show Answer
Correct Answer: B [ Only 1 & 2]
Notes:
Both obey the laws of reflection.
Both obey the laws of refraction.
Both travel with the speed of 3 × 108 ms–1.
Ultraviolet waves get readily scattered as compared to visible light
Ultraviolet waves are chemically more active than visible light
23. Consider the following statements:
- Speed of sound increases with increase in density of the medium
- Speed of sound increases with increase in temperature of the medium
Which of the above statements is/are correct?
[A] 1 Only
[B] 2 Only
[C] Both 1 & 2
[D] Neither 1 nor 2
Show Answer
Correct Answer: B [ 2 Only]
Notes:
When the elasticity of the medium increases the density decreases and it increases the sound speed. Higher temperatures lower the density of a medium, which puts less resistance on the sound waves.
24. Who among the following is credited to work for the unification of electricity, magnetism and optics field of Physics?
[A] James Clerk Maxwell
[B] Michael Faraday
[C] Haris Christian Oersted
[D] Isaac Newton
Show Answer
Correct Answer: A [James Clerk Maxwell]
Notes:
James Clerk Maxwell made the efforts for the unification of electricity, magnetism and optics field of Physics. He showed that light is an electromagnetic wave. James Clerk Maxwell was a Scottish mathematician, physicist and is known best for his mathematical work on electromagnetism and on the behaviour of gases.
25. Optical Fibre technology works on which of these principles of Physics?
[A] Bernoulli’s Principle
[B] Newton’s law of Motion
[C] Total internal reflection of Light
[D] Photoelectric effect
Show Answer
Correct Answer: C [Total internal reflection of Light]
Notes:
Optical Fibre technology works on the principle of Total internal reflection of Light. It helps in transmitting light signals from one place to another with a negligible loss of energy, thereby enabling to carry more signals than copper cables.
26. Which of the following is not a valid conservation law of classical Physics?
[A] Law of conservation of energy
[B] Law of conservation of current
[C] Law of conservation of angular momentum
[D] Law of conservation of charge
Show Answer
Correct Answer: B [Law of conservation of current]
Notes:
The following laws are dealt with in the classical physics: 1. Law of conservation of energy 2. Law of conservation of angular momentum 3. Law of conservation of linear momentum 4. Law of conservation of charge
27. What is the range of masses involved in the study of Physics?
[A] 10-19 kg to 1038 kg
[B] 10-30 kg to 1055kg
[C] 10-30 kg to 1030kg
[D] 10-19 kg to 1055 kg
Show Answer
Correct Answer: B [10-30 kg to 1055kg]
Notes:
The range of masses involved in the study of Physics ranges from 10-30 kg to 1055 kg. 10-30kg is the mass of an electron and 1055 kg is the mass of known observable universe. The range of time scale involved in the study of Physics ranges from 10-22 s to 1018 s. The range of length involved in the study of Physics ranges from 10-14m to 1026 m.
28. Who among the following is credited for the discovery of ‘Expanding Universe’?
[A] Edwin Hubble
[B] Niels Bohr
[C] S Chandra Shekhar
[D] C.V Raman
Show Answer
Correct Answer: A [Edwin Hubble]
Notes:
Edwin Hubble, an american astronomer, and was the first to prove that the universe is expanding. According to Expanding Universe theory, the universe is presently expanding. Hubble proved that there is a direct relationship between the speeds of distant galaxies and their distances from Earth. This is now known as Hubble’s Law.
29. Who among the following gave the Uncertainity principle?
[A] R.A Milkman
[B] Ernset Rutherford
[C] S.N Bose
[D] Werner Heisenberg
Show Answer
Correct Answer: D [Werner Heisenberg]
Notes:
Werner Heisenberg, a german Physicist, discovered the Uncertainity principle. As per the uncertainty principle, we cannot measure the position (x) and the momentum (p) of a particle with absolute precision. The more accurately we know one of these values, the less accurately we know the other. It represnts the effects of wave-particle duality on the properties of subatomic objects.
30. The force between charged particles is called as:
[A] Nuclear Force
[B] Gravitational Force
[C] Centrifugal Force
[D] Electromagnetic Force
Show Answer
Correct Answer: D [Electromagnetic Force]
Notes:
Electromagnetic force is the force between charged particles. It can be attractive for unlike charges and repulsive for like charges. It does not need any intervening medium to act and is enormously strong as compared to gravitational force.
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