This video lecture from Heat and Thermodynamics (F.Sc. first year physics) covers the concept of heat entrance rejection through a system and the work done on the system and by the system . and PV diagrams of work and the reason why work becomes positive and negative in some cases.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.