⚛️ Physics Quiz 13: Thermodynamics and Energy Transfer

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⚛️ Physics · Quiz 013

Apply conservation of energy to thermal systems and introduce the directional constraint supplied by the second law.

Learning goalUse the first law with a stated sign convention, distinguish simple processes, and interpret heat-engine efficiency without implying complete heat-to-work conversion.

  • 5 questions
  • Foundation
  • Explanations after finishing
Answered 0/5
FoundationUsing the convention that Q is positive for heat transferred into a system and W is positive for work done by the system, which equation states the first law of thermodynamics?
Need a small nudge?

Track which transfer adds energy to the system and which positive transfer removes energy from it.

UnderstandingWhy can a cyclic heat engine not convert all of the heat it absorbs from a hot reservoir into net work while returning to its initial state?
Need a small nudge?

The first law constrains energy accounting; the second law constrains the direction and complete convertibility of heat.

ApplicationA gas absorbs 500 J of heat and does 200 J of work on its surroundings. Using Delta U = Q - W, what is the change in the gas's internal energy?
Need a small nudge?

Insert Q = +500 J and W = +200 J into the stated first-law convention.

InterpretationAn ideal gas expands adiabatically and does 250 J of work on its surroundings. With Q = 0 and W positive for work done by the gas, what happens to its internal energy?
Need a small nudge?

Adiabatic means Q = 0, not Delta U = 0.

ConnectionA heat engine absorbs 1200 J from a hot reservoir and delivers 360 J of net work per cycle. Which pair is correct for its thermal efficiency and the heat rejected per cycle?
Need a small nudge?

Efficiency is W_out/Q_hot. Then use energy conservation over one complete cycle.

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