Heat and Temperature
Questions for Short Answer
Answer: If the temperature scale is not yet defined, it is not logical to say that a substance expands uniformly with the temperature.
Questions for Short Answer
1. If two bodies are in thermal equilibrium in one frame, will they be in thermal equilibrium in all frames?
Answer: Yes. The two bodies are in thermal equilibrium, it means that both have the same temperature. With the change of frame, the temperature of neither body will change.
2. Does the temperature of a body depend on the frame from which it is observed?
Answer: No, the temperature does not depend on the frame. It is not related to the motion of the body but is the state of the body which defines the level of hotness.
3. It is heard sometimes that mercury is used in defining the temperature scale because it expands uniformly with the temperature. If the temperature scale is not yet defined, is it logical to say that a substance expands uniformly with the temperature?
Answer: If the temperature scale is not yet defined, it is not logical to say that a substance expands uniformly with the temperature.
4. In defining the ideal gas temperature scale, it is assumed that the pressure of the gas at constant volume is proportional to the temperature T. How can we verify whether this is true or not? Are we using the kinetic theory of gases? Are we using the experimental result that the pressure is proportional to temperature?
Answer: Experimentally it can be verified that the pressure of the gas at constant volume is proportional to the temperature. In defining the Ideal Gas Temperature scale Kinetic theory of gases has not been used. We have used the experimental results "when the amount of the gas and hence pₜᵣ (pressure at the triple point) decreases the pressure is proportional to the temperature". i.e.
T = Lim{(p/pₜᵣ)*273.16} K, hen pₜᵣ→0.
5. Can the bulb of a thermometer be made of an adiabatic wall?
Answer: No. During the measurement of temperature, the bulb of the thermometer is brought in contact with the body so that both are in thermal equilibrium. To happen this the transfer of heat should be as quickly as possible. If the wall of the bulb is made adiabetic the heat transfer will not be possible and the temperature of the body can not be measured.
6. Why do marine animals live deep inside a lake when the surface of the lake freezes?
Answer: It is due to the unique character of the water that its density is maximum at 4 °C. Hence when the temperature falls below this point or to the freezing point, the water gets less dense and move towards the surface. Thus near the surface water freezes but near the bottom,, it is still liquid. Also, the ice (at the surface) is a bad conductor of heat, so it does not let the water below to freeze rapidly. Hence the marine animals live deep inside the lake in such a situation.
7. The length of a brass rod is found to be smaller on a hot summer day than on a cold winter day as measured by the same aluminum scale. Do we conclude that brass shrinks on heating?
Answer: No. The coefficient of linear expansion of aluminum is more than the brass. Hence the aluminum scale elongates more than the same length of brass on a hot summer day. Thus the length of the brass rod is found smaller. Not that brass shrinks on heating.
8. If mercury and glass had equal coefficients of volume expansion, could we make a mercury thermometer in a glass tube?
Answer: No. In this situation, both the glass bulb and the mercury will have the same expansion in the shape with the temperature increase and the mercury will not move in the capillary tube. Thus such a thermometer can not be made.
9. The density of water at 4°C is supposed to be 1000 kg/m³. Is it the same at the sea level and at a high altitude?
Answer: The density of water depends on the pressure. With the increase in pressure, the density also increases. The given density of water relates to the pressure at the sea level. Since at a high altitude, the pressure is less than the sea level the density of the water at 4 °C will be less than 1000 kg here.
10. A tightly closed metal lid of a glass bottle can be opened more easily if it is put in hot water for some time. Explain.
Answer: When the closed metal lid is put in hot water, the metal lid expands more than the glass. Thus it becomes loose and opens easily.
11. If an automobile engine is overheated, it is cooled by putting water on it. It is advised that the water should be put slowly with the engine running. Explain the reason.
Answer: Overheated automobile engine parts are expanded compared to the normal temperature state. If the water is put suddenly then there will be an uneven contraction in the engine parts. It will cause huge internal stress and the engine parts may get cracks. To avoid this the overheated engine is cooled slowly by slow putting of water with the engine running.
12. Is it possible for two bodies to be in thermal equilibrium if they are not in contact?
Answer: Yes, thermal equilibrium means both the bodies have the same temperature. Suppose two bodies are not in contact but each one is put in a heat reservoir. For example, two metal balls are placed in a room for a long time then each one will be in thermal equilibrium with the surrounding air. Now both the balls will be in thermal equilibrium without contact.
13. A spherical shell is heated. The volume changes according to the equation Vθ = V₀(1+ɣθ). Does the volume refer to the volume enclosed by the shell or the volume of the material making up the shell?
Answer: It is the volume enclosed by the shell including its thickness. The reason can be understood by taking a solid sphere and thinking it made up of reducing radius spherical shells that are kept inside without a gap. Now when the temperature changes, the volume changes according to the solid sphere. At the same time, the different shells making it also changes the volume as if it were a solid. So the volume referred to in this problem is the volume enclosed by the shell.
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Links to the Chapters
Links to the Chapters
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- 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
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CHAPTER- 7 - Circular Motion
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CHAPTER- 6 - Friction
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CHAPTER- 6 - Friction
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CHAPTER- 5 - Newton's Laws of Motion
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CHAPTER- 4 - The Forces
The Forces-
"Questions for short Answers"
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CHAPTER- 3 - Kinematics - Rest and Motion
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CHAPTER- 2 - "Physics and Mathematics"
CHAPTER- 2 - "Physics and Mathematics"
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