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Reviewed CSCA Physics question · Standard

A gas in a cylinder with a movable piston absorbs 650 J of heat from its surroundings. During the process, the gas expands and does 280 J of work on the piston. What is the change in internal energy of the gas?

  1. -370 J
  2. 370 J
  3. 930 J
  4. -930 J
Show the answer and explanation

Correct answer

B. 370 J

Principle or equation

The first law of thermodynamics: ΔU = Q - W, where Q is heat added to the system and W is work done by the system.

Why this answer is correct

Here Q = +650 J (heat absorbed) and W = +280 J (work done by gas). So ΔU = 650 J - 280 J = 370 J. The internal energy increases by 370 J.

Example

If a gas absorbs 100 J and does 40 J of work, ΔU = 100 - 40 = 60 J.

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