# PHY101 GDB Solution Feb 2015

The topic for the discussion is:
A room has one wall made of concrete, one wall made of copper, and one wall made of steel. All of the walls are the same size and at the same temperature of 20. Which wall feels coldest to the touch?
Select below the best choice according to your understanding and write the reason of your selected choice as well.
The copper wall
The steel wall
The concrete wall
All three wall equally cold to the touch
Elaborate your answer by giving a solid reason, give mathematical calculation (proof) where necessary.
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Solution : when you touch one of the walls, heat flows from your hand to the lower-temperature wall. The more rapidly heat flows from your hand, the colder you will feel. Recall that the rate of heat flow is proportional to the thermal conductivity. Note also that, copper has a much higher thermal conductivity (385.0W/m’K) than steel (50.2W/m’K) or concrete (0.8 W/m. K), and so the copper wall feels the coldest to the touch.