page 2-4
2. Hot metal

Hot to cold
If you were standing near an Electric Arc Furnace when the steel is poured, you would feel pretty hot. This is because the hot furnace is sending out infra red radiation. This is part of the electromagnetic spectrum.

When the infra red radiation hits your face or hands, it is absorbed and warms you up. The hotter the molten steel, the more intense the radiation and the hotter you will feel.

A white villa in the Sun. It keeps cool inside.

Picture 9. The house looks bright and white because it scatters so many visible light rays. It also scatters the infra red rays and therefore stays cool inside.

The Sun
The Sun is like a huge, extremely hot furnace out in space. We rely on it to keep the Earth warm. However, space is a vacuum so it can’t heat us up using conduction and convection. Instead, the energy is carried from the Sun by infra red radiation which can travel across the vacuum of space.
Keeping cool
Often we want to protect ourselves from radiation (including the Sun’s rays). We can do this by wearing white or shiny clothing. In hot countries, people paint their houses white to keep them cool inside.

The infra red radiation bounces off a white surface in the same way that light is reflected. So the shiny surface stops the radiation being absorbed.

Some solar panels. Painted black to absorb infra red radiation.
Picture 10. A roof of solar panels. Why are they black?
Photo courtesy of The Centre for Alternative Technology, Wales.
Absorbing the Sun's rays
On the other hand, a dull, black surface will absorb lots of radiation. They look black because no light is scattering off their surface - it is all absorbed. Similarly, they absorb infra red radiation, which warms them up.

Solar panels are painted black so that they absorb the infra red radiation from the Sun.

Question 2-4.

a) Look at the table below. There is one blank. Fill in the blank with the correct word (make sure you spell it correctly). Then select the best description in the last column.

Heat transfer method Method of transfer
infra red waves
b) Look at the sentences below. Select the correct option from the lists.
Radiation is absorbed best by surfaces. To keep cool in hot sunshine, you should wear clothing.
Summary                   Close
  • Radiation is made from infra red waves
  • It is like "radiant heat"
  • Infra red radiation is part of the electromagnetic spectrum
  • Black surfaces absorb radiation well
  • White, shiny surfaces scatter radiation and stay cool