TestUstad

Thirty joules of heat flow into a system. The system in turn does 50 Joules of work. The internal energy of the system has:

Correct answer: D. Decreased by 20 joules

  • A. Increased by 80 joules
  • B. Decreased by 80 joules
  • C. Increased by 20 joules
  • D. Decreased by 20 joules

Explanation

Using the first law of thermodynamics, ΔU = Q - W. Here, heat flows in, so Q = +30 J, and the system does work, so W = +50 J. Therefore, ΔU = 30 J - 50 J = -20 J, indicating the internal energy has decreased by 20 joules.

Written and checked by , contributorLast updated
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.

Start a free Thermodynamics testAll Thermodynamics MCQs

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.

Lecturer Physics Test Physics80 MCQsSubject Specialist Physics Test Physics80 MCQsNET Physics60 MCQsNUMS Physics40 MCQsDUHS Physics36 MCQsETEA MDCAT Physics36 MCQsKMU Physics36 MCQsMDCAT Physics36 MCQsECAT Physics30 MCQsETEA Engineering Admission Test Physics30 MCQsGIKI Physics30 MCQsNED Physics30 MCQsPIEAS Physics30 MCQsPMD Physics25 MCQsBSN Entry Test Physics20 MCQsPAF Airman Physics15 MCQs

More First Law of Thermodynamics questions

A container is divided into two equal portions. One portion contains an ideal gas at pressure P and temperature T while the other portion is a perfect vacuum. If a hole is opened between two portions:

Refrigerator is an example of:

The process which is performed quickly is

For the adiabatic process, the first law of thermodynamics is:

In a certain process, 400 J of heat energy is supplied to a system, and at the same time, 150 J of work is done by the system. The increase in internal energy of the system is

All the heat supplied to a system is converted into work in the process.