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Deepanshu posted an Question

May 16, 2020 • 03:52 am

30 points

IIT JAM
Physics (PH)

How do we calculate the efficiency of the reversible engine?

3 Answer(s)

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Ruby negi

A to B is isothermal process(dT=0) so temperature is same.. B to C is isobaric process for dQ=nCpdT and C to A is isochroic process so dQ=nCvdT(dW=0)...
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Ruby negi Best Answer

hope all steps are clear to you.. for any doubt please ask..
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Deepanshu Chaudhary

Im not getting that how the ratio W/Q can be found?
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wait a minute. I will give you exact method to do this question without Cv and Cp.
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ok thanks
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Dhairya sharma

in these type of question arrows should be given.
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Now how is efficiency greater than 1?
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that's why we will call it impossible heat engine.
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m saying this type ir irreversible engine are not possible they can be reversible only with efficiency 1.
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hope u get it ?
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Dhairya sharma

is it clear dear ?
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Dhairya sharma

dear bcoz it's reversible process and chnz in internal energy is o so work done will equal to heat absorbed. so efficiency of ideal reversible heat engine is one.
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But the place where I saw this question, 1 was not in the option. The options were like 1/3, 1/6 , etc. I don't have the question right now.. I guess the engine is not reversible
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yes if it is not reversible then we get the solution.
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if we finds the solution from the above question it will give efficiency more then one which is impossible . see the attached
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Dhairya sharma

like this. see the attached you will get it.
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what about heat mam? how can we get it from diagram?
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Dhairya sharma

for any process we have to calculate work done in any process. in your diagram we can calculate work done from area under the curve. that area will give us work done hence we will able to calculate efficiency.
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Abhishek singh

you can calculate the work done by area under the curve (area of triangle is 1/2* base * height.) and the heat intake can be calculated in isobaric and isochoric process. devide the two. to get the efficiency.
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heat will be CvdT and CpdT. But we have not been given the atomicity of the gas used. so how can we calculate it?
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Dhairya sharma

carnot engine is reversible heat engine. we can calculate its efficiency . see the attached
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I know this formula, but from the pv diagram how can we calculate?
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ok dear i give you full explanation.
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