An Ideal gas undergoes a four step cycle as shown in P-V diagram below . During this cycle …

Q: An Ideal gas undergoes a four step cycle as shown in P-V diagram below . During this cycle , heat is absorbed by the gas in

IIT

(a) Steps 1 and 2

(b) Steps 1 and 3

(c) Steps 1 and 4

(d) Steps 2 and 4

Click to See Solution :
Ans: (c)

Sol:Process 1:

P = constant , Volume increases and temperature also increases

Q = W + ΔU

W = +ve , ΔU = positive

Heat is positive and supplied to the gas

Process 2 :
V = constant , Pressure decreases

T ∝ P , (V = constant )

Temperature decreases , W = 0
ΔT is negative and ΔU = f/2 nRΔT

ΔU is also negative

Q = ΔU + W

Heat is negative and rejected by gas

Process 3 :
P = constant , Volume decreases

Temperature also decreases

W = PΔV = negative

ΔU = f/2 (nRΔT) = negative

Heat is negative and rejected by gas

Process 4 :
V = constant , Pressure increases

W = 0
PV = n RT => temperature increases

ΔU = f/2 (nRΔT) is positive

ΔQ = ΔU + W = Positive