Measuring Thermal Conductivity in Different Materials
Different materials (such as glass, steel, copper, and bubble gum) conduct heat at different rates, so the thermal conductivity constant depends on the material in question. Lucky for you, physicists have measured the constants for various materials already. This table shows some of these values.
Here’s an example of how conductivity affects heat transfer. The thermal conductivity of the steel part of a pot handle is
Now take a look at the figure.
Suppose the handle is 15 centimeters long, with a cross-sectional area of 2.0 square centimeters
If the fire at one end is 600 degrees Celsius, how much heat would be pumped into your hand in 1 second if you grabbed the handle? The equation for heat transfer by conduction is
If you assume that the end of the cool end of the handle starts at about room temperature, 25 degrees Celsius, you get the following amount of heat transferred in a time t:
You can see that in 1 second, 10.7 joules of thermal energy would enter your hand.
If 10.7 joules of heat is being transferred to the end of the handle each second, then the heat transfer is 10.7 joules per second, or 10.7 watts. As the seconds go by, the joules of heat add up, making the handle hotter and hotter. Note that the conduction rate of 10.7 watts will decrease with time because the end of the handle heats up, giving you a smaller value for
Eventually, however, an equilibrium is reached between the heat being transferred by conduction and the heat lost from the handle by radiation and by conduction losses to the surrounding air.