Transfer of HeatTransfer of HeatContinuedContinued

Last class we learned about two Last class we learned about two ways in which heat is transferred. ways in which heat is transferred. These areThese are

ConductionConduction ConvectionConvection

The third way in which heat is The third way in which heat is transferred is by transferred is by radiationradiation

Both conduction and convection Both conduction and convection require the movement of particles to require the movement of particles to transfer heat.transfer heat.

Radiation does not involve particles. Radiation does not involve particles. It is the It is the transfer of energy transfer of energy through invisible waves given off through invisible waves given off by an energy sourceby an energy source..

The heat from the sun is an example The heat from the sun is an example of radiation. This heat is transferred of radiation. This heat is transferred by invisible by invisible infrared wavesinfrared waves. .

All hot solids (including you!), liquids All hot solids (including you!), liquids and gases radiate invisible heat and gases radiate invisible heat waves. Infrared cameras are able to waves. Infrared cameras are able to form images of this heat.form images of this heat.

Uses of infrared imaging:Uses of infrared imaging: Satellites can detect infrared waves Satellites can detect infrared waves

given off by objects on earth. This given off by objects on earth. This can be used to track pollution and can be used to track pollution and weather.weather.

Infrared images can be Infrared images can be used in healthcareused in healthcare

And can be used to And can be used to monitor the health of monitor the health of the environment.the environment.

How radiant energy warms up How radiant energy warms up objects:objects:

When invisible waves of radiant When invisible waves of radiant energy come in contact with a solid, energy come in contact with a solid, the particles in the solid gain energy the particles in the solid gain energy and vibrate more quickly. The solid and vibrate more quickly. The solid heats up.heats up.

The solid also reradiates some of the The solid also reradiates some of the energy back into the surrounding energy back into the surrounding area.area.

Coloured solids absorb radiant Coloured solids absorb radiant energy, but clear solids, liquids and energy, but clear solids, liquids and gases just allow it to pass through.gases just allow it to pass through.

That’s why the seats That’s why the seats of your car can get of your car can get very hot on a summer very hot on a summer day, while the day, while the windows themselves windows themselves remain cool to touch.remain cool to touch.

Add the following words to Add the following words to your glossary, and write the your glossary, and write the

definition for each:definition for each:

RadiationRadiation Infrared waveInfrared wave

Homework:Homework:Write the following questions in your Write the following questions in your

notebook and answer them:notebook and answer them: In what state of matter can In what state of matter can

conduction occur?conduction occur? Can convection occur in both liquids Can convection occur in both liquids

and gases? Suggest a reason for and gases? Suggest a reason for your answer using particle theory.your answer using particle theory.

List two things that happen when List two things that happen when radiant energy waves contact a radiant energy waves contact a solid.solid.