The first law of thermodynamics is mathematically expressed as:
A$dQ = dU + dW$
B$dQ = dU - dW$
C$dU = dQ \cdot dW$
D$dQ \cdot dU = dW$
Answer & Solution
Correct answer: A. $dQ = dU + dW$
The first law states that heat $dQ$ supplied to a system goes into changing its internal energy $dU$ plus doing work $dW$ on the surroundings. So $dQ = dU + dW$. It is just energy conservation applied to thermodynamic systems.
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