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Absolute Zero

An object placed in a refrigerator is made colder by the refrigerator because the refrigerator removes energy from the object. How cold can an object be? The lowest temperature possible is called absolute zero. No energy can be obtained from an object at this temperature. The pressure of a gas would be zero at absolute zero, provided the gas did not liquefy as it was cooled. By measuring the pressure of a fixed amount of gas at steam point, then at ice point, the temperature for zero pressure can be estimated. This temperature is -273°C. No matter which gas or how much gas is used, the same value is always obtained for absolute zero. 

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Absolute zero temperature is a theoretical concept, it cannot apply in practical sense. Because if a body is at absolute zero means that all heat is removed from that body. It is not practical. So absolute zero is an imaginary concept. Anyway it is a lower limit of the temperature. This statement is related to the third law of thermodynamics. So many scientists try to get more closer value of absolute zero temperature. The third law has still never been violated experimentally. It becomes more difficult to lower the temperature of a material the closer the temperature gets to absolute zero. The difficulty increases with each step to the point at which an infinite amount of work would be required to reach the very bottom of the temperature scale. 

What happens at Absolute Zero?

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According to kinetic theory, if the temperature of a gas is reduced, the molecules move more slowly. As a result, they strike the container walls with less force, so the pressure drops. If you could go on cooling a gas, its molecules would eventually stop moving and cause no pressure. This would happen at -273°C. This is the lowest possible temperature and it is called absolute zero. 

Absolute Zero Pressure

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Pressure is the normal force exerted by a fluid per unit area. Pressure has a magnitude but no specific direction, expect that it acts normal to the surface. Pressures can be measured with reference to the atmospheric pressure or an absolute zero. In the first case, the atmospheric pressure is considered as zero and if the measured pressure is above atmospheric pressure, we say that the gauge pressure is positive. Similarly, if the pressure below atmospheric pressure, the gauge pressure is negative and it is a vacuum. The maximum vacuum pressure one can generate is one atmospheric pressure. This corresponds to absolute zero pressure. There can be no pressure below the absolute zero pressure. 

Temperature Limits

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It has long been known that there is a coldest possible temperature, called absolute zero, the temperature of an object if all heat could be removed from it. On the Fahrenheit temperature scale, absolute zero is about 460 degrees below zero. On the absolute or Kelvin temperature scale, absolute zero temperatures is assigned the value 0. Absolute zero is a temperature that can be approached but never actually reached. At temperatures approaching absolute zero, some metals become increasingly able to conduct electricity, with efficiencies approaching 100% ,a state called superconductivity. 
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