Sunday, February 3, 2008

JEE Revision - First law of thermodynamics

First law of thermodynamics;

Energy cannot be created or destroyed.

Energy can neither be created or nor destroyed although it can be converted from one form into another.

The energy of a system that isolated from its surroundings is constant.

Mathematical expresson for the first law

ΔU = q + w
q = heat added to the sytem
w = work done on the system

Sign conventions for heat and work

When w and q are positive, the internal energy increases. It means that energy is supplied to the system.

When w and q are negative, the internal energy decreases. It means that energy has left the system.

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