WTMA Heat Transfer and Conduction 3 — Questions and Answers
Question 1: A thermos keeps liquid hot by having a vacuum between its walls. The vacuum mainly prevents heat loss by:
- Conduction and convection (Correct answer)
- Radiation only
- Evaporation only
- Chemical reaction
Correct answer: Conduction and convection
A vacuum eliminates the medium needed for conduction and convection, preventing both modes of heat transfer.
Question 2: Heat flows from a hot object to a cool object. What happens when they reach the same temperature?
- Heat continues to flow from hot to cool
- Heat flow stops because there is no temperature difference (Correct answer)
- Cool object starts sending heat back
- Heat reverses direction spontaneously
Correct answer: Heat flow stops because there is no temperature difference
Heat transfer stops when thermal equilibrium is reached—no temperature difference means no net heat flow.
Question 3: A steel bolt conducts more heat than a rubber gasket of the same size because steel has:
- Lower density
- Higher thermal conductivity (Correct answer)
- Greater hardness
- More surface area
Correct answer: Higher thermal conductivity
Thermal conductivity is the material property that determines how well a substance conducts heat.
Question 4: Which situation would cause heat to conduct most rapidly through a wall?
- Thick wall, small temperature difference
- Thin wall, large temperature difference (Correct answer)
- Thick wall, large temperature difference
- Thin wall, small temperature difference
Correct answer: Thin wall, large temperature difference
Conduction rate increases with larger temperature differences and decreases with greater thickness.
Question 5: A machinist touches both a metal workbench and a rubber mat at the same room temperature. The metal feels colder because:
- The metal is actually at a lower temperature
- Metal conducts heat away from the hand faster (Correct answer)
- Rubber generates more heat
- The rubber reflects heat back to the hand
Correct answer: Metal conducts heat away from the hand faster
Metal's high conductivity draws heat from your skin rapidly, creating the sensation of cold even at the same temperature.
Question 6: In a car engine, coolant fluid carries heat away from the engine block to the radiator. This is primarily:
- Conduction
- Radiation
- Convection (Correct answer)
- Evaporation
Correct answer: Convection
Moving fluid carrying heat from one place to another is the definition of convection.
Question 7: What happens to the rate of heat conduction through a metal rod if you increase the temperature difference between its ends?
- Rate decreases
- Rate stays the same
- Rate increases (Correct answer)
- Rate becomes zero
Correct answer: Rate increases
According to Fourier's Law, heat conduction rate is directly proportional to the temperature difference.
WTMA Heat Transfer and Conduction 3
A thermos keeps liquid hot by having a vacuum between its walls.
The vacuum mainly prevents heat loss by: