Friday, February 8, 2008

IIT JEE Physics Formula Revision 26. Laws of Thermodynamics

First law of thermodynamics and its applications (only for ideal gases) 26.1;

26.1 ΔU = ΔQ - ΔW or

ΔQ = ΔU + ΔW

26.2 ΔW =∫pΔV from V1 to V2

26.3 Work done in an Isothermal process:
W is given by the expression nRTln[V2/V1]

Work doen in an Isobaric process - pressure is constant

W = p[V2 - V1]

Work done in an isochoric process: volume is constant. No work is done by the system.

4. Efficiency of an engine

η = W/Q1 = 1 - Q2/Q1

Q1 = Amout of heat taken by the engine
Q2 = Heat rejected by the engine to low temperature bodies

5. Entropy

∆S = ∆Q/T

6. Sf - Si = ∫∆Q/T from i to f

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