Question Details

One mole of a monatomic ideal gas undergoes the cyclic process J→ K→ L→ M→ J, as shown in the P-T diagram.

Match the quantities mentioned in List-I with their values in List-II and choose the correct option.

[ℛ is the gas constant.]

List-I List-II
(P) Work done in the complete
cyclic process
(1) R T 0 4 R T 0 l n 2
(Q) Change in the internal energy
of the gas in the process JK
(2) 0
(R) Heat given to the gas in the
process KL
(3)  3 R T 0
(S) Change in the internal energy
of the gas in the process MJ
(4)  2 R T 0 l n 2

(5)  3 R T 0 l n 2

Options

A

P → 1; Q → 3; R → 5; S → 4

B

P → 4; Q → 3; R → 5; S → 2

C

P → 4; Q → 1; R → 2; S → 2

D

P → 2; Q → 5; R → 3; S → 4

Show Answer

Correct Answer :

Option B

P → 4; Q → 3; R → 5; S → 2

P → 4; Q → 3; R → 5; S → 2

Solution :

Correct Option: P → 4; Q → 3; R → 5; S → 2

Let us analyze the cyclic process for n=1 mole of a monatomic ideal gas as shown in the pressure-temperature (P-T) diagram.
For a monatomic ideal gas:
The molar heat capacity at constant volume is:
C V = 3 2 R
The molar heat capacity at constant pressure is:
C P = 5 2 R

1. Analysis of individual processes:

Process J → K: Isobaric heating
From the diagram, the pressure is constant at P0, and the temperature increases from T0 to 3T0.
The change in internal energy (ΔUJK) is given by:
Δ U J K = n C V Δ T = 1 3 2 R ( 3 T 0 T 0 ) = 3 R T 0
Thus, (Q) → (3).
The work done during this process is:
W J K = n R Δ T = 1 R ( 3 T 0 T 0 ) = 2 R T 0

Process K → L: Isothermal compression
From the diagram, the temperature remains constant at 3T0, and the pressure increases from P0 to 2P0.
Since the temperature is constant, the change in internal energy is ΔUKL=0.
The heat given to the gas (QKL) is equal to the work done (WKL):
Q K L = W K L = n R T ln P i P f = 1 R ( 3 T 0 ) ln P 0 2 P 0 = 3 R T 0 ln 2
Thus, (R) → (5).

Process L → M: Isobaric cooling
The pressure is constant at 2P0, and the temperature decreases from 3T0 to T0.
The work done during this process is:
W L M = n R Δ T = 1 R ( T 0 3 T 0 ) = 2 R T 0

Process M → J: Isothermal expansion
The temperature remains constant at T0, and the pressure decreases from 2P0 to P0.
Since this is an isothermal process, the change in internal energy is:
Δ U M J = 0
Thus, (S) → (2).
The work done in this process is:
W M J = n R T ln P i P f = 1 R T 0 ln 2 P 0 P 0 = R T 0 ln 2

2. Work done in the complete cyclic process:
The net work done (W) is the sum of the work done in each stage:
W = W J K + W K L + W L M + W M J
Substituting the calculated work values:
W = 2 R T 0 3 R T 0 ln 2 2 R T 0 + R T 0 ln 2
Simplifying:
W = 2 R T 0 ln 2
Thus, (P) → (4).

Conclusion:
Matching the items from List-I with List-II:
P → 4
Q → 3
R → 5
S → 2
This corresponds directly to the option: P → 4; Q → 3; R → 5; S → 2.

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