Figure 14-20 shows an idealized situation in which conduction takes place. The cylinder of length \(L\) and cross-sectional area \(A\) is in thermal contact at one end with a hot region at temperature \(T_{\mathrm{H}}\) and in thermal contact at the other end with a cold region at temperature \(T_{\mathrm{C}}\). Experiment shows that the rate of heat transfer is proportional to the temperature difference \(T_{\mathrm{H}} - T_{\mathrm{C}}\) (the greater the temperature difference, the more rapidly heat flows). The rate of heat trans- fer is also greater if the cylinder is short (\(L\) is small) and wide (\(A\) is large). We can put these observations together into a single equation: