Question

some thermal mugs have layers of materials to keep drinks hot for as long as possible. which combination of layers would work best for this purpose?
a. inner core of steel, no air gap, outer layer of plastic
b. inner core of steel, air gap, outer layer of plastic
c. inner core of glass, air gap, outer layer of plastic
d. inner core of steel, no air gap, outer layer of glass

Explanation:

To keep drinks hot for as long as possible, we need to minimize heat transfer. Steel is a better conductor of heat than glass, so a steel inner core can better retain heat initially. An air - gap is a good insulator as air is a poor conductor of heat. Plastic is also a good insulator. Option A has no air - gap, so heat can transfer more easily. Option D has no air - gap and glass (a relatively poor conductor compared to steel for retaining heat in this context) as the outer layer. Option C has a glass inner core which is not as good as steel for retaining heat. Option B has a steel inner core (good for initial heat retention), an air - gap (good insulator), and a plastic outer layer (good insulator).

Answer:

B. Inner core of steel, air gap, outer layer of plastic