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Light and the Electromagnetic Spectrum

Emitting and absorbing thermal radiation

  • 3 things to know
  • Paper 1

Overview

How the intensity and wavelength of radiation change as a body gets hotter, infrared from everyday objects, the Sun and the Earth, and investigating emission and absorption by surfaces with a Leslie cube, a radiant heater and covered beakers.

What you need to know

Answer each one before you reveal it.

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Key term

State which objects emit electromagnetic radiation because of their temperature.

Key term

Describe how the intensity of the radiation emitted by a body changes as the body gets hotter.

Key term

Describe how the wavelengths emitted by a body change as the body gets hotter.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State which objects emit electromagnetic radiation because of their temperature.

    Model answer

    Every body emits radiation, whatever its temperature.

  2. 2

    Describe how the intensity of the radiation emitted by a body changes as the body gets hotter.

    Model answer

    A hotter body emits more radiation each second, so the intensity increases.

  3. 3

    Describe how the wavelengths emitted by a body change as the body gets hotter.

    Model answer

    The emission shifts towards shorter wavelengths, so more of it comes out at the short-wavelength end.

  4. 4

    Explain why a metal bar glows dull red and then orange-white as it is heated further.

    Model answer

    As its temperature rises it emits shorter wavelengths as well, so visible light is added to the infrared it already gave out.

  5. 5

    State the main type of electromagnetic radiation emitted by objects at everyday room temperature.

    Model answer

    Infrared radiation.

  6. 6

    Explain why a thermal imaging camera can find a person in complete darkness.

    Model answer

    The person's body emits infrared radiation because of its temperature, and the camera detects that radiation.

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