This video lecture from Heat and Thermodynamics (F.Sc. first year physics) covers 2nd law of thermodynamics with the example of heat engine, its efficiency and mechanical work. Also you will learn that how different machines work on that principle and method to calculate its efficiency. Find more e-learning material and educational video lectures in Urdu at maktab.pk. These videos are free to use for promotional and commercial purpose by keeping the credits to Maktab.