The laws of thermodynamics and heat engines
Grade 11 Science Worksheet - Challenge Me
Circle the best answer, or write your answer on the line.
A model heat engine runs between a hot side at 227 °C and a cold side at 27 °C. What is its greatest possible efficiency, to 0.1%, Ari?
A model heat engine runs between a hot side at 100 °C and a cold side at 20 °C. What is its greatest possible efficiency, to 0.1%, Bo?
A model heat engine runs between a hot side at 527 °C and a cold side at 127 °C. What is its greatest possible efficiency, to 0.1%, Esme?
A test report says a model engine running between 100 °C and 20 °C is 60% efficient. Is that possible, Jun?
- Yes: good engines can reach 60%
- No: its limit is about 21%
- Yes, if it runs long enough
Which change raises a heat engine's Carnot limit, Kira?
- A bigger engine at the same temperatures
- A hotter hot side
- A warmer cold side
Why must the temperatures in the Carnot limit be in kelvins, Luz?
- Kelvins are bigger units than degrees Celsius
- Celsius can't measure hot engines
- The ratio must count from absolute zero
Milo says a perfect engine with no friction could turn all its heat into work. Agree or disagree?
- Agree: without friction, nothing is wasted
- Disagree: some heat must go to the cold side
- Agree: the first law allows it, so it can happen
Noah says a car engine's waste heat is energy lost from the universe. Agree or disagree?
- Agree: engines use up energy
- Disagree: the heat still exists in the surroundings
- Agree: wasted energy is gone for good
Pia says a toy Stirling engine can run forever on one cup of hot water. Agree or disagree?
- Disagree: it stops when the cup cools to room temperature
- Agree: it turns the cup's heat into work again and again
- Agree: the engine makes its own heat
A model engine between 227 °C and 27 °C has a Carnot limit of 40%. Tests show 28%. Why is it lower, Ren?
- Real engines can beat the limit
- Friction and heat leaks waste extra energy
- The limit was worked out in Celsius