Questions for Short Answer
1. The speed of light in glass is 2.0x10⁸ m/s. Does it violate the second postulate of special relativity?
ANSWER: The second postulate of special relativity states that "The speed of light in vacuum has the same value c in all the inertial frame". Here the light is traveling in a medium glass, not in a vacuum. Hence the second postulate of special relativity is not violated.
The second postulate is also confirmed by Maxwell's equation for the speed of light in a vacuum. Here,
c =1/√(µₒ𝜀ₒ)
Since µₒ and 𝜀ₒ will be different for glass, the speed of light will be different in it.
2. A uniformly moving train passes by a long platform. Consider the events "engine crossing the beginning of the platform" and "engine crossing the end of the platform". Which frame (the train frame or the platform frame) is the proper frame for the pair events?
ANSWER: The frame in which the two events occurred at the same place is the proper frame. Since the platform is very long, the given two events occur in the same place at the engine. For the platform, the two events occur at two places i.e. at the beginning and at the end of the platform. Hence the train frame is the proper frame for the pair of events.
3. An object may be regarded to be at rest or in motion depending on the frame of reference chosen to view the object. Because of length contraction, it would mean that the same rod may have two different lengths depending on the state of the observer. Is this true?
ANSWER: Yes, it is true. The length measured by the observer in a frame at rest with the object is called its rest length' or 'proper length'. The length measured by an observer in a moving frame with respect to the object is shorter in length and by a factor 𝜸 than its rest length.
4. The mass of a particle depends on its speed. Does the attraction of the earth on the particle also depend on the particle's speed?
ANSWER: The attraction of the earth on a particle is the gravitational force on the particle by the earth. Since the law of gravitation states that the force of the gravitation between two objects is proportional to the mass of each object, the attraction of the earth on the given particle also depends on the mass of the particle which is itself dependent on its speed.
Note: Dependence of mass on the speed
This is the reason that a particle can not be given a speed approaching the speed of light whatever force we apply. Because as the speed increases the mass also increases it requires more force to accelerate (F =ma). As the speed approaches c, mass approaches infinity according to this relativistic mass,
m =mₒ/√{1-(v²/c²)}.
It means an infinite force is needed to accelerate it.
5. A person traveling in a fast spaceship measures the distance between the earth and the moon. Is it the same, smaller, or larger than the value quoted in the book?
ANSWER: It depends on which direction the spaceship is going. Consider the distance between the earth and the moon as a rod and the spaceship is traveling perpendicular to this rod. Since this rod is moving perpendicular to its length with respect to the spaceship, the length L remains unchanged as quoted in the book.
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| Figure for Q-5 |
Now consider that the spaceship is moving along the line joining the earth and the moon. Now the rod is moving parallel to its length with respect to the spaceship. Its length will be measured contracted by a factor 𝜸, where 𝜸 =1/√(1 -v²/c²). So the contracted length L' =L/𝜸.
If the spaceship is moving in any other direction its contracted length will be between L and L'.
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Links to the Chapters
Links to the Chapters
CHAPTER- 45- Semiconductors and Semiconductor Devices
CHAPTER- 44- X-raysCHAPTER- 43- Bohr's Model and Physics of AtomCHAPTER- 42- Photoelectric Effect and Wave-Particle DualityCHAPTER- 41- Electric Current Through Gases
CHAPTER- 40- Electromagnetic WavesCHAPTER- 39- Alternating CurrentCHAPTER- 38- Electromagnetic Induction
CHAPTER- 37- Magnetic Properties of MatterCHAPTER- 36- Permanent Magnets
CHAPTER- 35- Magnetic Field due to a Current
CHAPTER- 34- Magnetic Field
CHAPTER- 33- Thermal and Chemical Effects of Electric Current
CHAPTER- 45- Semiconductors and Semiconductor Devices
CHAPTER- 44- X-rays
CHAPTER- 43- Bohr's Model and Physics of Atom
CHAPTER- 42- Photoelectric Effect and Wave-Particle Duality
CHAPTER- 41- Electric Current Through Gases
CHAPTER- 40- Electromagnetic Waves
CHAPTER- 39- Alternating Current
CHAPTER- 38- Electromagnetic Induction
CHAPTER- 37- Magnetic Properties of Matter
CHAPTER- 36- Permanent Magnets
CHAPTER- 35- Magnetic Field due to a Current
CHAPTER- 34- Magnetic Field
CHAPTER- 33- Thermal and Chemical Effects of Electric Current
CHAPTER- 32- Electric Current in ConductorsCHAPTER- 31- CapacitorsCHAPTER- 30- Gauss's Law
CHAPTER- 29- Electric Field and Potential
CHAPTER- 28- Heat Transfer
OBJECTIVE -I
CHAPTER- 26-Laws of Thermodynamics
CHAPTER- 25-CALORIMETRY
Questions for Short Answer
OBJECTIVE-I
OBJECTIVE-II
EXERCISES - Q-11 to Q-18
CHAPTER- 24-Kinetic Theory of Gases
CHAPTER- 23 - Heat and Temperature
CHAPTER- 21 - Speed of Light
CHAPTER- 20 - Dispersion and Spectra
CHAPTER- 19 - Optical Instruments
CHAPTER- 18 - Geometrical Optics
CHAPTER- 17 - Light Waves
CHAPTER- 16 - Sound Waves
CHAPTER- 15 - Wave Motion and Waves on a String
CHAPTER- 14 - Fluid Mechanics
CHAPTER- 13 - Fluid Mechanics
CHAPTER- 12 - Simple Harmonic Motion
CHAPTER- 11 - Gravitation
CHAPTER- 10 - Rotational Mechanics
CHAPTER- 9 - Center of Mass, Linear Momentum, Collision
CHAPTER- 32- Electric Current in Conductors
CHAPTER- 31- Capacitors
CHAPTER- 30- Gauss's Law
CHAPTER- 29- Electric Field and Potential
CHAPTER- 28- Heat Transfer
CHAPTER- 26-Laws of Thermodynamics
CHAPTER- 25-CALORIMETRY
Questions for Short Answer
OBJECTIVE-I
OBJECTIVE-II
CHAPTER- 24-Kinetic Theory of Gases
CHAPTER- 23 - Heat and Temperature
CHAPTER- 21 - Speed of Light
CHAPTER- 20 - Dispersion and Spectra
CHAPTER- 19 - Optical Instruments
CHAPTER- 18 - Geometrical Optics
CHAPTER- 17 - Light Waves
CHAPTER- 16 - Sound Waves
CHAPTER- 15 - Wave Motion and Waves on a String
CHAPTER- 14 - Fluid Mechanics
CHAPTER- 13 - Fluid Mechanics
CHAPTER- 12 - Simple Harmonic Motion
CHAPTER- 11 - Gravitation
CHAPTER- 10 - Rotational Mechanics
CHAPTER- 9 - Center of Mass, Linear Momentum, Collision
CHAPTER- 8 - Work and Energy
Click here for → Question for Short Answers
Click here for → OBJECTIVE-I
Click here for → OBJECTIVE-II
Click here for → Exercises (1-10)
Click here for → Question for Short Answers
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Click here for → OBJECTIVE-II
Click here for → Exercises (1-10)
Click here for → Exercises (11-20)
CHAPTER- 7 - Circular Motion
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Click here for → EXERCISES (11-20)
Click here for → EXERCISES (21-30)
CHAPTER- 6 - Friction
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Click here for → OBJECTIVE-I
Click here for → OBJECTIVE-II
Click here for → EXERCISES (11-20)
Click here for → EXERCISES (21-30)
CHAPTER- 6 - Friction
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Click here for → Questions for Short Answer
Click here for → OBJECTIVE-I
Click here for → Friction - OBJECTIVE-II
Click here for → EXERCISES (1-10)
Click here for → Exercises (11-20)
Click here for → EXERCISES (21-31)
Click here for → OBJECTIVE-I
Click here for → Friction - OBJECTIVE-II
Click here for → EXERCISES (1-10)
Click here for → Exercises (11-20)
Click here for → EXERCISES (21-31)
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CHAPTER- 5 - Newton's Laws of Motion
Click here for → QUESTIONS FOR SHORT ANSWER
Click here for → QUESTIONS FOR SHORT ANSWER
Click here for→ Newton's laws of motion - Objective - I
Click here for → Newton's Laws of Motion - Objective -II
Click here for → Newton's Laws of Motion-Exercises(Q. No. 1 to 12)
Click here for→ Newton's laws of motion - Objective - I
Click here for → Newton's Laws of Motion - Objective -II
Click here for → Newton's Laws of Motion-Exercises(Q. No. 1 to 12)
Click here for→Newton's Laws of Motion,Exercises(Q.No. 13 to 27)
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CHAPTER- 4 - The Forces
The Forces-
"Questions for short Answers"
Click here for "The Forces" - OBJECTIVE-I
Click here for "The Forces" - OBJECTIVE-II
Click here for "The Forces" - Exercises
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CHAPTER- 3 - Kinematics - Rest and Motion
Click here for "Questions for short Answers"
Click here for "OBJECTIVE-I"
Click here for EXERCISES (Question number 1 to 10)
Click here for EXERCISES (Question number 11 to 20)
Click here for EXERCISES (Question number 21 to 30)
Click here for EXERCISES (Question number 31 to 40)
Click here for EXERCISES (Question number 41 to 52)
CHAPTER- 2 - "Physics and Mathematics"
CHAPTER- 2 - "Physics and Mathematics"
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