Page 172 - Science Coursebook

11.6 Radiation

You have learnt about conduction and
convection, two ways in which energy can
be transferred from a hotter place to a
colder place. Here is a third.

A butterfly cannot fly until its temperature

reaches 16 °C. On a cold day, it will find a

sunny spot and sit with its wings open.

The butterfly is absorbing energy from the
Sun’s rays. If you sit in a sunny spot, you
may get too hot as you, too, will absorb
energy from sunlight.

This butterfly is basking in the sunlight in the
Ghanaian rainforest.

Energy from the Sun

The Earth receives a lot of energy from
the Sun. How does it get here?

It cannot travel by conduction or
convection because it has to pass through a
vacuum (empty space) to get here. There is
no matter in space.
Instead, it travels as infra-red radiation.
Infra-red radiation is similar to light,
except that it is invisible to our eyes.
Anything which is warm gives out infra-
red radiation. The hotter it is, the more
energy it radiates. Anything which absorbs
radiation gets warm.

Infra-red radiation can travel through Infra-red radiation brings us energy from the Sun. At
empty space and through any transparent night, the Earth cools down.
material such as air or glass.

Questions

A+I 1 If you stand in front of a hot oven, you will get warm. Is its energy reaching
you by conduction, convection or radiation? Explain your answer.
A+I 2 It is easy to understand why it gets warmer during the day – the Earth is
absorbing radiation from the Sun. But why does it cool down at night? Where
is the Earth’s energy going?

170 11 Energy

A+E