brodidit for students
Home / Practice / ECAT / Physics / Heat and thermodynamics
Heat and thermodynamics
5 ECAT Physics questions with answers and explanations.
-
For a fixed mass of ideal gas in a rigid container, doubling the absolute temperature will:
- 1 Halve the pressure
- 2 Double the pressure
- 3 Leave the pressure unchanged
- 4 Quadruple the pressure
Show answer
Correct answer: Double the pressure
At constant volume, pressure is proportional to absolute temperature (Gay-Lussac's law).
-
What is the efficiency of a Carnot engine working between 500 K and 300 K?
- 1 60%
- 2 20%
- 3 40%
- 4 80%
Show answer
Correct answer: 40%
Efficiency = 1 - T_cold / T_hot = 1 - 300/500 = 0.4, which is 40%.
-
The average kinetic energy of the molecules of an ideal gas is proportional to:
- 1 Pressure
- 2 Absolute temperature
- 3 Volume
- 4 Mass of the gas
Show answer
Correct answer: Absolute temperature
The mean kinetic energy per molecule equals 3/2 kT, where T is the absolute temperature.
-
How much heat is needed to melt 0.5 kg of ice at 0 degrees C? (Latent heat of fusion = 334 kJ/kg)
- 1 167 kJ
- 2 334 kJ
- 3 668 kJ
- 4 83.5 kJ
-
In an isothermal process for an ideal gas, the change in internal energy is:
- 1 Positive
- 2 Negative
- 3 Zero
- 4 Equal to the work done on the gas
Show answer
Correct answer: Zero
Internal energy of an ideal gas depends only on temperature, and the temperature does not change.