Plenary Questions

PFY p.54

1

a) Thermal energy travels through the bottom of a pan by convection. The energy is passed from one vibrating atom to the next. All metals are good conducts. Plastic, water and air are poor conductors (good insulators)

b) Convection currents can form when liquids and gases are heated. The cold fluid falls and the hot fluids rises.

c) Energy can travel through empty space by radiation rays, which can be reflected by mirror like light rays. Dull black surfaces are good radiators and good absorbers. Shiny, bright surfaces are good radiators and bad absorbers.

d) A vacuum flask uses silvering to cut down heat transfer by conduction and uses a vacuum to cut down heat transfer by convection and radiation.