According to the first law of thermodynamics, ΔU = Q + W, where ΔU Is the increase in internal energy of the system, Q is the heat transferred to the system and W is the external work done by the system.Which of the following is NOT a correct expression?
Correct answer: D. When work is done by the system: ΔU = Q - W
- A. At constant temperature: Q = -W
- B. When no work is done: ΔU = Q
- C. In gaseous system: ΔU = Q + P Δ V
- D. When work is done by the system: ΔU = Q - W
Explanation
There are two sign conventions:1. ∆U= Q+W: Here, work done BYthe gas/system is taken POSITIVE. 2. ∆U= Q-W: Here, work done ON the gas/system is taken NEGATIVE. The equation provided in the question follows the first convention, according to which D is incorrect.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? [email protected]
About First Law of Thermodynamics
The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.
Practise Thermodynamics
714 free Thermodynamics MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Physics questions like this
Physics is on 16 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More First Law of Thermodynamics questions
The bicycle pump works based on:
The efficiency of a Carnot engine increases when:
The work done in an adiabatic process is given by:
The efficiency of the Carnot's Engine working between 150°C and 50°C is:
A system absorbs 1000 Joules of heat and delivers 600 Joules of work, while losing 100 Joules of heat by conduction to the atmosphere, the change in the internal energy of the system will be:
The equation ΔU = ΔQ refers to: