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P1 Topic 2 The electromagnetic spectrum
The discovery of infrared

William Herschel was a British astronomer. He put dark, coloured filters on his telescopes (to help him
observe the sun safely) and noticed that different coloured filters heated up his telescope to different
extents. He wondered whether the different colours…

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The full range of electromagnetic waves is called the electromagnetic spectrum. It includes all waves we can
and cannot see.
The spectrum is continuous which means all values of wavelength are possible. It is convenient to group the
spectrum into seven wavelength groups, as shown in figure B.
Modern astronomy…

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Short-wave radio signals can be received from long distances from the transmitter, but for a different
reason. They can be reflected from the ionosphere (an electrically charged layer of the Earth's atmosphere).
Medium-wave signals can also reflect from the ionosphere, depending on the atmospheric conditions and
time of day.

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Cameras use a lens to focus visible light onto a light-sensitive film or electronic sensor that records the image.
The lens' aperture determines how much light enters the camera. The shutter speed determines how long
the film is exposed to the light.
By controlling the aperture and shutter speed, the…




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