(a) State the three processes of thermal energy transfer by which a hot object cools down.
(b) Of the three processes in (a), which one of them
(i) involves thermal energy travelling from the hot object to its surroundings without heating the air around it? Why?
(ii) occurs only in fluids (ie liquids or gases)? Why?
(c) Metals are good conductors of heat whereas wood is a poor conductor of heat (i.e. an insulator).
Discuss this statement with reference to the mechanism of thermal energy transfer in solids.
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Answer:
(a) Conduction, convection, radiation.
(b)
(i) Radiation. Radiation is the only process that does not need a medium to transfer the energy. The energy can be transferred through vacuum. Hence, it can travel without heating the air around it.
(ii) Convection. It occurs by means of convection currents set up in fluids due to differences in density.
(c) For conduction of heat within solids, the two mechanisms are molecular vibrations and free electron diffusion. Since metals contain many free electrons, they transfer heat faster.
