Download conceptual physics

Transmission of Heat
 Conduction of heat
 Takes place within certain materials and from one of
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these materials to another when they are in direct
contact.
Conductors: metals- silver, copper, aluminum and iron
Insulators: delay the transfer of heat. Ex. Wood, cork,
styrofoam
Poor conductors are good insulators.
Liquids and gases in general are good insulators. Snow is
a good insulator (has a lot of air)
Insulation delays the transfer of heat.
Cold is the absence of heat.
 Convection: heating occurs by currents in a fluid
(liquid or gas)
 Convection is an application of archimedes principle. If
a fluid is heated from below, it expands and becomes
less dense and rises.
 Winds: result from convection currents that stir the
atmosphere.
 Radiation
 Heat from the sun warm’s
the earth’s surface through
radiation.
 Energy that is transmitted by
radiation is called radiant energy.
Heat_Transmission__Conduction__Convection__and_Ra
diation.asf
 Forms of radiant energy: radio waves, microwaves,
infrared, visible light, ultraviolet, X rays, and gamma
rays.
 Absorption of radiant energy
 Good absorbers of radiant energy reflects very little
radiant energy, including light. Thus, appears black. Ex.
Pupil of eye
 Good reflectors are poor absorbers. Light colored
objects reflect more light and heat than dark-colored
ones.
 Emission of radiant energy
 Good absorbers are good emitters; poor absorbers are
poor emitters.
 Ex. A radio antenna built to emmit radio waves, will also
be a good receiver of radio waves.
 Whether a surface plays the role of emitter or absorber
depends on whether its temperature is above or below
room temperature.
 Read p329.
 Newton’s Law of cooling
 The rate of cooling of an object depends on how much
hotter the object is than the surroundings.
 Newton’s Law of cooling states:
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The rate of cooling of an object- whether by conduction,
convection, or radiation- is approximately proportional to the
temperature difference, T, between the object and its
surroundings.
 The greenhouse effect
 Radiant energy from the sun warms the earth. And earth
emits terrestrial radiation which most escapes to outer
space.
 Much of terrestrial radiation is absorbed by water vapor
and carbon dioxide in the atmosphere.
 Effects_of_Global_Warming_on_Alaska.asf
Transmission of Heat