Wednesday, February 7, 2018

How does a refrigerator works?

Second Law of Thermodynamics states that if a cold object is placed near a hot object, the temperature of colder object will rises and the temperature of warmer object will fall.

so how it practically works..............

It works on principal of cooling through evaporation.

An evaporating gas called refrigerant draws heat from the surrounding and make it cold.
there is a compressor which imparts high pressure to the refrigerant (pure Ammonia is used commonly which evaporates at -32 Celsius). Due to this high pressure its temperature increases and it becomes hot. This heated gas flow through the coil, behind the refrigerator which allows excess heat to be released in surrounding (this is the reason of feeling warmer around the fridge).



eventually the ammonia cools down to the point where it becomes liquid. then it passes through an expansion valve.due to a very small opening the liquid ammonia is turned into a very cold, fast moving mist.Since this evaporation occur at -32 Celsius the ammonia draw heat from the surrounding.
This the second law of thermodynamics where the cold ammonia take heat from the object which is placed in refrigerator (say a water bottle) and makes the object cooler. As it takes heat it temperature rises and then this warm ammonia is returned back to compressor and the cycle continues where the pressurization, evaporation and cooling begins.

Tuesday, January 23, 2018

Why the earth pin is made bigger in a three pin plug

first of all know the reason for this third pin.

when we use an appliances of metal body there is a chance of possible electric shock due to some charge leakage inside the appliance.
hence to prevent electric shock there proper earthing is required which is done by this third pin.

Now the reason behind making this pin bigger.
Earth pin is longer than the others which means it is first to connect as well as last to disconnect.



  • when inserting the plug, the earth connection is made before the current carrying contact of the plug become live.

  • when removing the plug, the current carrying contact separate before the earth connection is separate. 
Thus it is always made to improve safety.