Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: If and represent the heat supplied to the system and the work done on the system respectively. Then according to the first law of thermodynamics .
Reason R: First law of thermodynamics is based on law of conservation of energy.
In the light of the above statements, choose the correct answer from the options given below:
Assertion A: If and represent the heat supplied to the system and the work done on the system respectively. Then according to the first law of thermodynamics .
Reason R: First law of thermodynamics is based on law of conservation of energy.
In the light of the above statements, choose the correct answer from the options given below:
- A.Both A and R are correct and R is the correct explanation of A
- B.A is correct but R is not correct
- C.A is not correct but R is correct
- D.Both A and R are correct but R is not the correct explanation of A
Show answer and solution
Correct option: A
Solution
When work dW is done on the system, the internal energy increases, so the first law becomes dU = dQ + dW, which rearranges to dQ = dU - dW. This sign convention (work done on system is positive) is consistent and valid, making Assertion A correct. The first law is fundamentally a statement of conservation of energy — the heat added to a system goes into changing its internal energy and/or doing work — so Reason R correctly explains the thermodynamic basis of Assertion A.
[JEE Main 2023 · 29 Jan · Shift 1]