Page 173 - Science Coursebook

11.6 Radiation

Good and bad radiators
Matt (not shiny) black surfaces are good at radiating heat
energy. That is why the inside of an oven is often painted
black – then, as it heats up, it radiates energy at the food.

Shiny white or silver surfaces reflect radiation, just as they

reflect light. This shows that it is difficult for radiation to pass
through a shiny surface.
This means that shiny surfaces are poor absorbers of
radiation – it reflects off them. It also means that shiny

surfaces are poor emitters of radiation – energy escapes only
slowly from a hot, shiny object.
The seats in this car are black. The

Question driver has fitted a sunshield inside the
windscreen.
A+I 3 Explain why the car in the photograph would get hot
on a sunny day. How will the sunshield help to keep
the car cool?

Activity 11.6
Conduction, convection and radiation

SE If you put hot water in a container, it will
gradually cool down.
Set up a number of different containers,

similar to those shown in the picture.
They could be made of metal, glass,
plastic or cardboard. The outer surface
may be black, white or silver. Some should
have a lid.
Pour boiling water into each and add a
thermometer. Record each temperature as
the water cools.
Analyse your results. Can you say whether
the energy is escaping from the water by
conduction, convection or radiation?

Summary
• Energy can be transferred through a vacuum or transparent
substance by infra-red radiation.
• Matt black surfaces are good at absorbing radiation.
• Shiny surfaces are good at reflecting radiation.

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