Radiation

LESSON 4

Energy Transfer

Conduction

Convection

Radiation

energy can be transferred in three ways

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Conduction

Conduction is the transfer of thermal energy through contact between substances

• the substances need to be in direct contact in order �for the energy to transfer

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Convection

• convection is the transfer of thermal energy through circulating currents in a fluid

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Radiation

• radiation is the transfer of energy by means of electromagnetic waves

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Radiation

• radiation is the transfer of energy by means of electromagnetic waves
• Non-contact

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Conduction, Convection, Radiation

CONDUCTION

CONVECTION

RADIATION

both convection and conduction require contact between the substances

but radiation transfers heat without contact

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Radiation

• when you stand near a campfire, the heat that you feel reaches you through radiation
• you become warm without touching the fire because it emits heat energy that travels through the air towards you

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RADIANT ENERGY

Radiant Energy

Radiant energy reaches Earth from the sun

• it travels via electromagnetic waves �through empty space
• the sun emits both visible rays (light rays) �and invisible rays (ultraviolet rays)
• the energy is emitted in all directions but only a small fraction of these reach Earth

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Radiant Energy

Matter both absorbs and emits radiant energy

• the sand on a beach absorbs the energy �from the sun and increases in temperature
• the sand feels hot to our feet because it also emits radiant heat energy back out
• the heat energy that is emitted is made of invisible rays called infrared rays

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WAVELENGTHS

Wavelengths

• the different types of energy are created by different wavelengths
• the longer the wavelength, the lower the energy carried on the wave

WAVELENGTH

WAVELENGTH

• SHORT WAVELENGTH
• HIGH FREQUENCY
• HIGH ENERGY

• LONG WAVELENGTH
• LOW FREQUENCY
• LOW ENERGY

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100 000 000 000 000 000 000

10 000 000

100 000 000 000

0.000000001

SOLAR

RADIATION

Solar Radiation

of the incoming solar radiation from the sun, some is absorbed and some is reflected

51% ABSORBED BY SURFACE (LAND & WATER)

19% ABSORBED BY ATMOSPHERE & CLOUDS

4% REFLECTED BY SURFACE (LAND & WATER)

20% REFLECTED BY CLOUDS

6% REFLECTED BY ATMOSPHERE

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Solar Radiation

70% Absorbed

• this energy stays within the Earth’s system and warms it

30% Reflected

• this energy does not stay within the Earth’s system and does not warm it

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Solar Radiation

WHICH SHIRT IS BETTER TO WEAR ON A HOT TRACK & FIELD DAY?

WHY?

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Solar Radiation

• the amount of energy that will be absorbed or reflected depends on the material that the sunlight strikes
• darker colours absorb more energy
• lighter colours or shiny surfaces �absorb less energy

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Solar Radiation

WHICH SHIRT IS BETTER TO WEAR ON A HOT TRACK & FIELD DAY?

WHY?

ABSORBS

HEAT

REFLECTS

HEAT

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