P1 1.1 1.2 Infrared Radiation

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P1 1.1 Infrared Radiation
Learning Objectives
• Understand what infrared radiation is.
• Know the factors that affect the amount of
infrared radiation emitted or absorbed by an
object.
•Explain how infrared radiation can be used.
Starter: Where and how is heat transfer
taking place at this seaside?
• Barbecue grill cooking burgers and sausages (conduction, radiation).
• The car bonnet is so hot that as a sideline to the barbecue,
someone is cooking food on it (conduction).
• Picnic boxes labelled “cold” and “hot” contain items that have been
kept cool and warm, respectively, to prevent heat transfer taking
place.
• The twins on the left are wearing identical clothing except that one
is wearing a white t-shirt and keeping cool, while the other is
wearing a black t-shirt and looking much hotter (radiation).
• The twin in the black t-shirt is trying to keep himself cool with a
portable fan (convection).
• The fluttering sails on the boat out at sea and the fluttering flag
on the flagpole show that it is windy at the seaside (convection).
• The ice-creams are melted very quickly by the heat of the Sun,
much to the annoyance of the child near the ice-cream van
(radiation).
What does this camera show?
Transferring energy
• If two objects are at different temperatures
e
will be transferred from the h
to
the cooler object, until they are both the
s
temperature.
This can happen in different ways
• Infrared radiation
• Conduction
• Convection
Infrared radiation
• Energy can travel through
materials or
through a vacuum as IR. IR transfers energy
by
waves. Infrared waves are similar to
waves, except that we cannot see them.
• Everything
and absorbs IR. The
amount of IR absorbed or emitted by a body
depends on its temperature and the nature of
its surface.
Light, Emits, Electromagnetic, Transparent
Emitting and absorbing infrared
radiation.
• Q) Design a table showing which items of the
school uniform are good and bad in the summer
and the winter, with reasons for this?
• A surface will reflect some of the infrared
radiation that reaches it, and absorb the rest.
• Light coloured, shiny surfaces are good at
reflecting radiation, so they are poor at
absorbing it. Dark, matt surfaces are good at
absorbing radiation.
• Surfaces that are good at absorbing radiation
are also good at emitting it. Dark matt surfaces
are good emitters of radiation, and light shiny
surfaces are poor emitters.
http://www.youtube.com/watch?v=2--0q0XlQJ0
1. What is the image?
2. What is it?
3. It’s a zebra. But in visible light,
what colour are the stripes that look
white in infrared?
4. What is it?
5. Why would someone want an
infrared image of their house?
6. Why does the lizard look so
different in colour from the hand in
this infrared picture?
7. Here you can see infrared waves
doing something that all types of
wave can do. What?
Quick Quiz
1. Do all objects emit infrared radiation?
2. Cross out the incorrect words: The
(hotter/cooler) an object is the (more/
less) infrared radiation it radiates in a
given time.
3. What kind of surfaces are good emitters
of infrared radiation?
4. What kind of surfaces are poor emitters
of infrared radiation?
Planning an experiment
• Plan a class experiment to:
“To measure the temperature of hot
water cooling in shiny and dark cans”.
– Discuss what the independent, dependent
and controlled variables are.
– What is the fair test for this investigation?
– Make a prediction.
– Draw a labelled diagram of your experiment.
– Write a method to explain what you would do.
– What would you expect to happen?
– Design a results table.
Copy and complete:
• If two objects made from the same material
have identical v_________, a thin, flat object
will radiate heat energy faster than a f____
object. This is one reason why domestic
radiators are t______ and flat.
• Radiators are often painted with w_______
gloss paint. They would be better at radiating
heat if they were painted with b______ matt
paint, but in fact, despite their name,
radiators transfer most of their heat to a
room by c___________.
Plenary
• Explain why marathon runners
are wrapped in foil blankets
following a race.
• Explain why kettles are light
coloured.
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