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Himanshu posted an Question
April 28, 2020 • 09:00 am 30 points
  • IIT JAM
  • Physics (PH)

Thermodynamics 2

Question in first pic and solutions in 2&3 1)My question is here we are calculating efficiency of what because the efficiency of Carnot's engine is coming simply 0.69 2) Question from 2nd pic how in Physics we take time as 1 like here taken W=Px1 ,for making P=W otherwise they are not equal 3) Question from 3rd pic how u make 40 K watt to 40 KJ by using 4 cycles in 1 sec??

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    Abhishek singh

    the explanation for question 3 is same as of question 2. regards.

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    Abhishek singh

    fir pic - 2 , we did all our calculations for one second (go to the question and the typed solution by me of the same question, you will get , what I am talking about) And for one second, Work is equal to power as (work = power * time, put time = 1 second, Work = Power). That why you can use the same value of power, for work ( as throughout the question, we did all calculations for one second). Best regards.

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    Abhishek singh Best Answer

    For the doubt from pic-1 : Why Carnot engine is special one? What makes it different from other heat engine? These are some doubts, you must have! Carnot engine is an ideal case, which is not practically possible. The reason is, we assume Carnot engine to be reversible, but no process in this universe is reversible! For any heat engine, you can use efficiency (n) = 1 - Q2/Q1. But you have a special form for efficiency for the case of reversible engine (i.e. Carnot engine) and the formula gets reduced to, n = 1- Q2/Q1 = 1- T2/T1. you can only use the temperature form for reversible ( or ideal or Carnot) engine. Now it's home work time for you. Check efficiency by both formulas in all four option. If efficiency by Temperature formula comes out to be greater than efficiency by Heat formula (i.e efficiency of reversible engine is greater than efficiency of normal heat engine, then it's possible, that respective option is acceptable as answer (i.e. option A and B)). Best regards.

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    Shanu arora best-answer

    here is detailed explanation I have tried to give you, I am sure after this there will not be by doubt of this sought , although you are always welcome for the doubts . talking of Carnot engine is an ideal engine which do not exist but in physics we study it thoroughly. feel free for more doubts .

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