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Physics Tutorial:Second Law of Thermodynamics and your Fridge

The Second Law of Thermodynamics is one of three Laws of Thermodynamics. The term

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"thermodynamics" comes from two main words "thermo," meaning heat, and "dynamic," meaning power. So, the Laws of Thermodynamics are the Laws of heat power. All things in the universe are affected by Laws of Thermodynamics. The Second Law of Thermodynamics states heat naturally tends to flow from a hot object to a cold object.


According to the Second Law of Thermodynamics, when heat is converted into mechanical work, only some of the heat available can be converted to work, the rest is dispersed into the surroundings.  In a car’s engine, burning fuel releases heat that expands the gases in the cylinders.  The expanding gases cause pistons to move.  Not all of the heat can be harnessed to move the pistons.  Some of the heat is expelled with the exhaust gases.





Question: How does the Second Law of Thermodynamics help in the working of a refrigerator?


Another way of stating the second law of thermodynamics is that work must be done to get heat to flow from a cold object to a hot object.  In a refrigerator there is a cycle that is carried on continuously. A liquid refrigerant substance vaporizes in the cooling coils inside the fridge. The fluid absorbs heat from its surroundings to vaporize. This cools the interior of the fridge. The gas thus formed is pumped to the exterior of the fridge where it is compressed into a liquid. Work is done on the gas to compress the gas, causing the gas to release heat. This heat is lost to the air surrounding the fridge. Hence, heat is moved from the inside of the fridge to the outside.


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