Machine-translated by Google. Questions are authored in English.
Top

Discussion

If Q1 and Q2 are respectively, the heat supplied and expelled by a system at a constant temperature, then the work done by the system is

  • A.\(Q_{1} - Q_{2}\)
  • B.\(Q_{1} + Q_{2}\)
  • C.\(\frac{Q_{1} - Q_{2}}{2}\)
  • D.\(\frac{Q_{2} - Q_{1}}{2}\)
  • E.\(\frac{Q_{1} + Q_{2}}{2}\)

Answer: A

The work done is \(Q_{1} - Q_{2}\).

By the first law, \(Q = \Delta U + W\). At constant temperature (for an ideal gas) or over a complete cycle, \(\Delta U = 0\), so the work done equals the net heat taken in: heat supplied \(Q_{1}\) minus heat given out \(Q_{2}\).

\(Q_{1} + Q_{2}\) adds the heat expelled instead of subtracting it, and the halved forms have no basis in the first law.

This is the same balance used for a heat engine over a cycle, where the efficiency is \(\frac{Q_{1} - Q_{2}}{Q_{1}}\).

No comment is present. Be the first to comment.
Loading…

Post your comment

Please log in or register to post a comment.