Diagram
TV plot of polytropic process and its variation with ratio of specific heat capacities
Diagram
PT plot of polytropic process and understand variation with ratio of specific heat capacities
Example
sources of Heat
The sun produces heat from nuclear reactions deep inside it. All life on the earth depends on this heat.
Friction -- the rubbing of one object against another -- produces heat. Survivalists (and Boy Scouts) learn to start a fire with friction.Chemical reactions produce heat by causing a chemical change in substances. The fire of a match is the result of a chemical reaction.
The Earth contains much heat deep inside. Some of this heat escapes to the surface when a volcano erupts.
Definition
Heat sink and heat source
A heat sink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device into a coolant fluid in motion.
A heat source is an object that produces or radiates heat.
A heat source is an object that produces or radiates heat.
Definition
Qualitative statement of Second Law of thermodynamics
Qualitative statement of Second Law of Thermodynamics:
It is not possible to design a heat engine which works in cyclic process and whose only result is to take heat from a body at a single temperature and convert it completely into mechanical work.
It is not possible to design a heat engine which works in cyclic process and whose only result is to take heat from a body at a single temperature and convert it completely into mechanical work.
Definition
Kelvin Planck statement
No process is possible whose sole result is the absorption of heat into a reservoir and its complete conversion into work.
Definition
Clausius statement
No process is possible whose sole result is the transfer of heat from a colder body to a hotter body.
Definition
Second Law in terms of efficiency
The second Law of thermodynamics gives a fundamental limitation to the efficiency of a heat engine and the co-efficient of performance of a refrigerator. In simple terms, it says that the efficiency of a heat engine can never be unity.
Example
Physical examples of Second Law of Thermodynamics
Physical examples of Second law of thermodynamics are as follows:
1. An internal combustion engine in a car converts chemical energy from the gasoline to heat to forward motion. The best efficiency we could get is something on the order of 35%, and that's the absolute best we can do, ignoring friction losses and the like. (The exact maximum efficiency is dependent on the temperature of the combustion and the heat sink, i.e. ambient).
2. Heat flows from bodies with higher temperature to the lower temperature and not vice versa.
3. Work can be converted completely into heat as in case of a resistor but heat cannot be completely converted into work as is in the case of a heat engine.
4. A drop of dye when placed in a beaker of water will eventually result in an evenly coloured solution, even without stirring. The dye molecules diffuse and spread itself as evenly as possible throughout the volume of water.
1. An internal combustion engine in a car converts chemical energy from the gasoline to heat to forward motion. The best efficiency we could get is something on the order of 35%, and that's the absolute best we can do, ignoring friction losses and the like. (The exact maximum efficiency is dependent on the temperature of the combustion and the heat sink, i.e. ambient).
2. Heat flows from bodies with higher temperature to the lower temperature and not vice versa.
3. Work can be converted completely into heat as in case of a resistor but heat cannot be completely converted into work as is in the case of a heat engine.
4. A drop of dye when placed in a beaker of water will eventually result in an evenly coloured solution, even without stirring. The dye molecules diffuse and spread itself as evenly as possible throughout the volume of water.
Definition
Identify whether a process follows or violates Second Law of Thermodynamics
The process which follow second law of thermodynamics:
1. A drop of dye when placed in a beaker of water will eventually result in an evenly coloured solution, even without stirring. The dye molecules diffuse and spread itself as evenly as possible throughout the volume of water.
2. Making snowballs will always make ones hands colder, because thermal energy always flows in a hot-to-cold direction. No material can spontaneously gain thermal energy from colder surroundings. This is because it would require the energy to become spontaneously more concentrated in order for the opposite process to occur. That is, this would involve a spontaneous increase in organization of molecules or energy which would mean the opposite of energy spreading out.A device that violates the Second Law of Thermodynamics is formally known as a perpetual motion machine of the second kind. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an energy source. This kind of machine is impossible, as it would violate the first or second law of thermodynamics.
1. A drop of dye when placed in a beaker of water will eventually result in an evenly coloured solution, even without stirring. The dye molecules diffuse and spread itself as evenly as possible throughout the volume of water.
2. Making snowballs will always make ones hands colder, because thermal energy always flows in a hot-to-cold direction. No material can spontaneously gain thermal energy from colder surroundings. This is because it would require the energy to become spontaneously more concentrated in order for the opposite process to occur. That is, this would involve a spontaneous increase in organization of molecules or energy which would mean the opposite of energy spreading out.A device that violates the Second Law of Thermodynamics is formally known as a perpetual motion machine of the second kind. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an energy source. This kind of machine is impossible, as it would violate the first or second law of thermodynamics.
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