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Himanshu posted an Question

April 30, 2020 • 08:42 am

30 points

IIT JAM
Physics (PH)

Thermodynamics

Which one is correct and why???? .

2 Answer(s)

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Himanshu Pandey

Abhishek sir if it is like that for heat look at Vaishali mam second pic where heat for irreversible is more and it also seems to be logical
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Abhishek singh

1) For your first doubt, Have you given a look at my 2nd and third attached in the same comment? In second attached Two graphs are given one for reversible and irreversible each. irreversible may take place in a single step(it means you increased the pressure suddenly and accordingly the volume gets decreased suddenly in response it is like putting a 10 Kg weight on the movable side of piston) for multiple step irreversible process I had attached third pic. you can assume it as putting 10, 1 kg weights one by one. But what is reversible process? you can assume it as putting 10 kg of sand, but each time a single sand partical only!, ideally even it is also not a reversible process(it would have been reversible if the mass of sand partical tend to zero)
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now see the graphs and compare yourself, area in multiple step is greater than area in single step. that's why we try to make as many steps as we can to approach reversibility.
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Himanshu Pandey

Abhishek sir clear me these things 1) underline of attachment regarding whole play of graph and multiple steps 2) For heat as dQ=dW if heat follow same trend as work done then why for irreversible it is more as which is opposite to that of work dome
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No, I never said heat is more for irreversible! you can again check my previous comments. And I am still saying, heat exactly following work trend. heat reversible is greater!
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Abhishek singh

Sometimes my solution gets disappeared even after posting it successfully. However here is the screenshot .
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Abhishek singh

I have something for you, which will give you a complete understanding of why workdone in reversible process is greater than irreversible process. Read them carefully. the graph in 2nd attached is for single step irreversible process and a reversible (infinite step) process. And the graph in 3rd attached is for multi step irreversible process and reversible (always infinite step, as ideal) process. Best regards
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Dhairya sharma Best Answer

solution
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