Engineering
Physics
Thermodynamics

Question

An ideal gas in undergoing a cyclic thermodynamic process in different ways as shown in the corresponding P – V diagram in column 3 of the table. Consider only the path from state 1 to state 2. W denotes the corresponding work done on the system. The equations and plots in the table have standard notations as used in thermodynamic processes. Here γ is the ratio of heat capacities at constant pressure and constant volume. The number of moles in the gas in n.

Column 1

Column 2

Column 3

(I) W1→2=1γ–1(P2V2–P1V1) 

(i) Isothermal

(II) W1→2=–PV2+PV1

(ii) Isochoric

(III) W1→2 = 0

(iii) Isobaric

(IV) W1→2=–nRTln(V2V1)

(iv) Adiabatic

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Linked Question 1

Which of the following options is the only correct representation of a process in which ΔU = ΔQ – PΔV?

(II) (iii) (S)

(II) (iv) (R)

(III) (iii) (P)

(II) (iii) (P)

Solution

Only B option is following the correct sequence of operations.

Linked Question 2

Which one of the following options correctly represents a thermodynamic process that is used as a correction in the determination of the speed of sound in an ideal gas ?

(III) (iv) (R)

(I) (iv) (Q)

(I) (ii) (Q)

(IV) (ii) (R)

Solution

For determination of speed of sound in an ideal gas we use adianatic process. So any option - C is matching.

Linked Question 3

Which one of the following options is the correct combination ?

(IV) (ii) (S)

(III) (ii) (S)

(II) (iv) (P)

(II) (iv) (R)

Solution

Isobaric → work done =ρσv

F.L.T. = Q = U + ω

⇒ W = adiabatic = 1r−1 (P2v2 – P1v1)

⇒ Wisochoric = ρdv = 0

⇒ Wisothermal ⇒ –nRT long (v2v1)