Teaching Physics with the Physics Suite Edward F. Redish Problems Sorted by Type | Problems Sorted by Subject | Problems Sorted by Chapter in UP

Baking a potato

 When baking a potato (white or sweet) in the oven, I find they come out much more uniformly cooked if I stick aluminum rods into the potato. (You can buy such rods in any kitchen supply store.) Why do you think this works? Because the aluminum has a much higher specific heat than the potato and so it holds a lot of thermal energy. Because the aluminum has a much lower specific heat than the potato and so it lets the potato have most of the thermal energy. Because the aluminum has a much higher thermal conductivity than the potato so putting the rods in brings the thermal energy into the center of the potato more quickly so it cooks more uniformly. Some other reason.

When I bake a sweet potato in the oven, I always put it on a thin sheet of aluminum foil. This is because sometimes the potato exudes a sugary juice that burns and makes a hard-to-clean-up mess if it drips on the bottom of the oven. When I’m ready to take the potato out of the hot (400o F) oven after an hour of cooking, I find I can pick up the aluminum foil with my bare hands without getting burned. Why do you think this is so?

1. Because the aluminum foil has a high specific heat so that it holds on to most of the thermal energy.
2. Because the aluminum foil has a low specific heat and not much mass, so even at a high temperature it doesn’t have a lot of thermal energy in it to burn me.
3. Because the aluminum foil has a low thermal conductivity so that although the foil is hot, the heat doesn’t flow into my hand.
4. Because the aluminum foil doesn’t get hot in the oven, even though the oven is at a high temperature.
5. Some other reason.