You simultaneously touch a metal frying pan and a wooden cutting board that have both been sitting in a 22°C kitchen. The metal feels much colder. What explains this?
AThe metal is actually at a lower temperature than the wood — metal loses heat to the air faster
BMetal has higher thermal conductivity, so it draws heat away from your hand faster, making it feel colder
CYour hand heats the wood, raising its temperature, while metal remains cold
DMetal has a lower heat capacity, so it absorbs less total energy from your hand
Both objects are at 22°C — the same temperature. 'Feeling cold' reflects the rate at which heat leaves your hand, not the object's temperature. Metal's high thermal conductivity (k) means it transfers heat away from your hand very rapidly, signaling coldness to your nerves. Wood's low k means heat flows slowly, so your hand doesn't cool quickly. The temperature is identical; the sensation differs entirely because k differs.
Question 2 Multiple Choice
A wall is 10 cm thick. If the thickness is doubled to 20 cm while everything else stays the same, what happens to the rate of heat conduction through it?
AThe rate doubles — more material provides more pathways for heat
BThe rate stays the same — thickness does not affect heat flow
CThe rate is halved — thickness L is in the denominator of Fourier's Law
DThe rate is quartered — the effect compounds with the area
Fourier's Law: P = kA(ΔT/L). Thickness L is in the denominator, so doubling L halves P. More thickness means heat must travel farther through the material, increasing thermal resistance R = L/(kA) and proportionally reducing the flow rate. This is the physical principle behind thick insulation.
Question 3 True / False
Two objects at exactly the same temperature can feel different temperatures when touched.
TTrue
FFalse
Answer: True
True — and this is the central insight of conduction. What you feel as 'cold' or 'warm' is not the object's temperature but the rate of heat flow between the object and your skin. A metal and a wooden object at the same temperature feel different because their thermal conductivities differ by orders of magnitude.
Question 4 True / False
Adding thicker insulation to a wall reduces heat loss mainly because the insulation is colder than the outside air.
TTrue
FFalse
Answer: False
False. Insulation works because of its low thermal conductivity (k) and because increasing thickness (L) raises thermal resistance R = L/(kA), reducing heat flow P = kA(ΔT/L). The temperature of the insulation is not the cause — what matters are the material property k and the thickness L. A thicker wall of any material reduces heat loss, regardless of the insulation's temperature.
Question 5 Short Answer
Why does doubling the thickness of an insulating wall reduce heat loss, and how does Fourier's Law explain this?
Think about your answer, then reveal below.
Model answer: Fourier's Law states P = kA(ΔT/L). Thickness L appears in the denominator, so doubling L doubles the thermal resistance (R = L/kA) and halves the heat flow rate P. Physically, heat must travel a longer path through more material, slowing the transfer of energy.
Thermal resistance R = L/(kA) works like electrical resistance: more resistance means less current (heat flow). Doubling L doubles R, halving P. This is why building codes specify minimum insulation thickness — each added inch meaningfully reduces energy loss in winter.