P005 Hot Puzzles

Here are some interesting physics puzzles that test your knowledge of chemical energy, thermal energy, …

Note that the effects to be considered may be quite small, but there is a difference nevertheless.

1. Which will give better mileage in a car — a litre of cold petrol or  a litre of warm petrol?

2. Two identical spheres of metal coated with an excellent thermal insulator are injected with the same amount of heat (say by converting chemical energy to heat inside each sphere). All other things are equal, except that one sphere is resting on a table, while the other is suspended from the ceiling. Which sphere will attain a higher rise in temperature?

3. Two drops of mercury at the same temparature, resting on a non-wetting flat thermal insulator, are slowly nudged together until they form one big drop. Will the temperature of the merged drop rise or fall in the process?

4.  An electric heater is turned on for a few minutes in a room so that the room temperature rises by a few degrees. If we measure the energy content of the air in the room before and after – which reading will be higher?

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