· Heat energy can be
transferred from one point to another by conduction, convection and
· Heat waves have
wavelengths in the order of 10-7 to 10-3m.
· No known surface is a
perfectly black body.
· Fery's absorber, which is a
double-walled, hollow sphere with a tiny hole or aperture, is a close
approximation of a perfectly black body.
· A body which neither
gains nor loses heat is said to be in a state of dynamical equilibrium.
· Newton's law of cooling gives
reasonably accurate results for temperature excess of about 40°C.
· Coefficient of absorption,
reflection, transmission and emission are all quantities with no unit.
· Radiation is the only mode of
transfer of energy that not require a medium.
· Conduction takes place mostly
in solids, while convection in liquids and gases.
· Newton's law of cooling can
be derived from Stefan's law, if the temperature excess is small.