HEAT ENERGY AND ITS TRANSFER. HEAT TRANSFER BY RADIATION.

HEAT ENERGY AND ITS TRANSFER

HEAT TRANSFER BYRADIATION

Learning PointsLearning Points 1. State that heat is transferred in straight lines in all directions by radiation.

2. State that heat rays are also known as infra-red rays.

3. Give examples of the uses of infra-red radiation.

• Heat energy waves (or rays) are known as Infrared Radiation.

• Infrared Radiation waves will travel out from a hot source in all directions.

Heater

Infrared Radiation

• Heat energy from the sun travels to earth by radiation.

• Since the space between the sun and the earth is a vacuum (no particles present), the heat cannot travel by conduction or convection.

Infrared Radiation

• Special Infrared cameras can be used to show the Infrared radiation given off by different objects.

Infrared Radiation pictures

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• This is a infrared image of a child’s hand holding a lizard.

• Lizards are reptiles and are cold blooded.

• Notice how the child`s hand is warm compared to the lizard.


• This is an infrared image of a person.

• What area is the hottest?

• What do you think it is?


• This is an infrared image of two coffee cups containing very hot drinks.



• This is a infrared image of a dear in the dark.

• Since infrared cameras detect heat radiation they can see the heat from warm blooded animals in the dark.

• This infrared medical scan shows an injured and healthy leg.

• The bright white region shows the location of the injury, which is warmer due to the increased blood flow to the injured area.


• This is a infrared image of footprints.

• As this person walks away barefoot the heat left behind her feet stills glows on the ground.


• This is an infrared image of a cat.

• The yellow areas are the warmest and the purple areas are cool.


• This is a infrared image of a tyre that has been heated by friction with the road.

• Notice how the area of the tyre that touches the road glows much more brightly when you look through the infrared camera.


• This is a infrared image of a zebra.

• Notice how the stripes appear on the infrared.

• Do you think these are the black or white stripes?


• This is an infrared image of a heating element.

• Even after the stove is turned off, this heating element will glow brightly in the infrared until it reaches room temperature.


• This is a infrared map of global sea surface temperatures.

• Infrared satellites are used to measure and track changing ocean surface temperatures to help predict weather patterns.


• Different surfaces will absorb different amounts of infrared radiation.

Radiation Absorbers and Emitters

-Dull, black surfaces are good absorbers of radiation.

-Light, shiny surfaces will reflect the radiation.

Vacuum Flask

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• A vacuum flask has a double wall of silvered glass with some vacuum between the wall.

• The silvered surfaces reflect the infrared radiation from the very hot contents back in to the flask.

• The vacuum between the outer and inner walls prevents heat loss through conduction.

Vacuum Flask

Quick Quiz

• What direction does radiation travel?

• Which will radiate more heat, black or shiny surfaces?

• Which will absorb more heat?

In all directions in a straight line

Black

Black

• What’s the other name for heat radiation?

• Give two uses for this radiation.

Infra-red

Infrared photographs, remote controls, heat seeking missiles, searching for earthquake survivors, chasing criminals, making toast, keeping homes warm…

Quick Quiz

Radiation

1. Put 5mls hot water into each test tube

2. Take the temperature at time ‘0’

3. Take the temperature of each test tube every minute for 10 minutes

4. What results would you expect? WhyGlass Black

paperSilver

foil

Radiation

• Thermal energy can travel in waves, a bit like light

• Waves do not need particles so:– They travel very fast (300 000km/sec)– They can travel through a vacuum (e.g. Space)– They can be reflected– They can not travel through opaque objects – the

energy gets absorbed instead

Visible Spectrum

Radiation – what have we learnt?

1. Copy and complete the following:The water in the test tube covered in black paper

cooled.....this is because...The water in the test tube covered in silver foil

cooled....this is because...2. Houses in hot countries are often painted

white – explain why you think this is.3. Polar bears actually have black skin beneath

their fur – explain why you think this is.

1. Conduction2. Convection 3. Radiation.

Heat Transfer-Summary

HEAT ENERGY AND ITS TRANSFER. HEAT TRANSFER BY RADIATION.

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