Here are two multiple choice questions on thermodynamics which appeared in AIPMT 2009 question paper:
(i) In thermodynamic processes which of the following statements is not true?
(1) In an isochoric process pressure remains constant
(2) In an isothermal process the temperature remains constant
(3) In an adiabatic process PVγ = constant
(4) In an adiabatic process the system is insulated from the surroundings
The only statement which is not true is statement (1). A process in which the pressure remains constant is called isobaric process (and not isochoric process).
[Note that an isochoric process is one in which the volume remains constant].
(ii) The internal energy change in a system that has absorbed 2 Kcals of heat and
done 500 J of work is:
(1) 6400 J
(2) 5400 J
(3) 7900 J
(4) 8900 J
When a quantity Q of heat is supplied to a system it is used to do an amount of work W by the system and to increase the internal energy of the system by ∆U:
Q = ∆U + W
Note that Q given in kilo calories is to be converted into joule which is the SI unit of heat. Therefore Q = 2×1000×4.2 J = 8400 J (remembering that 1 cal = 4.2 J very nearly).
The increase the internal energy, ∆U = Q – W =8400 – 500 = 7900 J.
Find some more multiple choice questions (with solution) in this section here as well as here.
