WTMA Heat Transfer and Conduction 5 — Questions and Answers
Question 1: A worker holds a copper wire in a flame. Within seconds the far end becomes too hot to touch. This happens because copper:
- Generates its own heat when stressed
- Has very high thermal conductivity (Correct answer)
- Melts and re-solidifies, releasing heat
- Converts radiation to conduction
Correct answer: Has very high thermal conductivity
Copper is one of the best thermal conductors among common metals, so heat travels quickly along its length.
Question 2: An oven mitt with thick padding protects a cook's hand by:
- Reflecting all radiated heat from the oven
- Providing a thick layer of low-conductivity material that slows heat transfer (Correct answer)
- Conducting heat away from the hand quickly
- Absorbing and storing heat indefinitely
Correct answer: Providing a thick layer of low-conductivity material that slows heat transfer
The thick, low-conductivity padding creates high thermal resistance, slowing heat flow to the hand.
Question 3: Two identical metal blocks—one at 200°F, one at 70°F—are placed in contact. Heat will flow:
- From the cooler block to the hotter block
- From the hotter block to the cooler block (Correct answer)
- In both directions equally
- No heat flows since both are solid
Correct answer: From the hotter block to the cooler block
Heat always flows spontaneously from higher temperature to lower temperature until equilibrium is reached.
Question 4: Which modification to a metal rod would MOST increase the amount of heat it can conduct per minute?
- Painting it black
- Increasing its cross-sectional area (Correct answer)
- Decreasing the temperature difference across it
- Wrapping it in fiberglass
Correct answer: Increasing its cross-sectional area
Larger cross-sectional area provides more pathways for heat to flow, increasing total conduction rate.
Question 5: A steam pipe is insulated with fiberglass wrap. Which statement is correct about the fiberglass?
- It conducts heat well and carries heat to the pipe surface
- It has low thermal conductivity, reducing heat loss to the surroundings (Correct answer)
- It reflects steam heat back into the pipe
- It absorbs heat from the environment and warms the pipe
Correct answer: It has low thermal conductivity, reducing heat loss to the surroundings
Fiberglass is an effective insulator because its low thermal conductivity greatly resists heat conduction outward.
Question 6: On a cold day, a metal fence post feels colder than a wooden fence post at the same outdoor temperature. This is because:
- The metal post is actually colder due to wind
- Metal conducts heat from your hand more rapidly than wood (Correct answer)
- Wood generates metabolic heat
- Metal has a lower surface temperature in sunlight
Correct answer: Metal conducts heat from your hand more rapidly than wood
Metal's high conductivity draws heat from your skin quickly, making it feel colder even at the same temperature.
Question 7: In heat conduction, the quantity called 'thermal resistance' increases when you:
- Use a material with higher thermal conductivity or make it thinner
- Use a material with lower thermal conductivity or make it thicker (Correct answer)
- Increase the temperature difference across the material
- Use a denser material regardless of conductivity
Correct answer: Use a material with lower thermal conductivity or make it thicker
Thermal resistance increases with thickness and decreases with conductivity—thicker, lower-conductivity materials resist heat flow more.
WTMA Heat Transfer and Conduction 5
A worker holds a copper wire in a flame.
Within seconds the far end becomes too hot to touch.
This happens because copper: