Heat and Thermodynamics 5 Question 5

5. Following figure shows two processes A and B for a gas. If ΔQA and ΔQB are the amount of heat absorbed by the system in two cases, and ΔUA and ΔUB are changes in internal energies respectively, then

(2019 Main, 9 April I)

(a) ΔQA>ΔQB,ΔUA>ΔUB

(b) ΔQA<ΔQB,ΔUA<ΔUB

(c) ΔQA>ΔQB,ΔUA=ΔUB

(d) ΔQA=ΔQB;ΔUA=ΔUB

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Answer:

Correct Answer: 5. (c)

Solution:

  1. According to the first law of thermodynamics,

Heat supplied (ΔQ)= Work done (W)+ Change in internal energy of the system (ΔU)

Similarly, for process B,

ΔQA=ΔUA+WA

Now, we know that,

ΔQB=ΔUB+WB

work done for a process = area under it’s p - V curve Here,

Thus, it is clear from the above graphs,

WA>WB(i)

Also, since the initial and final state are same in both process, so

ΔUA=ΔUB(ii)

So, from Eqs. (i) and (ii), we can conclude that

ΔQA>ΔQB



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