IIT JEE , AIEEE Forum - Physics , Thermal Physics

saurabhpanda

can any one tell me when to use Cp and Cv while calculating internal energy.

in adiabatic and polytropic process why do we say int. energy = nCv

t and not nCp

t?/??

(while we know that Cv is applied at const. vol. and Cp at const. press.)

why is then E=nCvdT applicable to all cases but nCpdT not????

aneeshrox

In an adiabatic process as you know that no heat is either given or let to escape because the system is isolated
thus if any heat change takes place
for example if we want to increase the temperature we increase the preasure in order to increase the temperature
as pressure is directly propotional
if any heat change take place due to system isolation it take the form of pressure
thats why volume is said to be constt and changes are made in pressure
thats why this formula of constt volume is used

joyfrancis

THE INTERNAL ENERGY CHANGE IS ALWAYS EQUAL TO NCVDELTAT IRRESPECTIVE OF THE TYPE OF PROCESS...IT IS CLEARLY KNOWN THAT DELTAU BECOMES ZERO IN ISOTHERMAL PROCESS.

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