Question 04: State the Second law of thermodynamics.
Answer: Second Law of Thermodynamics: This law states that, where there is a definite limit to the amount of mechanical energy which can be obtained from a given quantity of the heat energy.
Kelvin- Plank statement of second law:
“It is impossible to build a cyclic engine that converts thermal energy into work with 100% efficiency”.
From the figure, QH – QL = W.
From the statement, QH = W, QL = 0
But this is impossible.
Clausius Statement of Second law:
“It is impossible for an engine working in a cyclic process, to transfer heat from a body at a lower temperature to a body at a higher temperature without the aid of an external work done”.
Basically QH – QL = W, But
From the statement QH =Q; W = 0 But it is impossible.
Here, H.T.R = Higher Temperature Reservoir.
L.T.R = Lower Temperature Reservoir.