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Sound waves
Sound waves are longitudinal waves. Their vibrations occur in the same direction as
the direction of travel. Sound waves can only travel through a solid, liquid or gas.


Ultrasound waves have frequencies above about 20kHz (20,000Hz). This is above
the normal hearing range for humans, so we…

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Evidence from seismic waves
The speed of P waves and S waves increases as they travel deeper into the
mantle. They travel through the Earth in curved paths, but they change direction
suddenly when they pass through the boundary between substances in different
states. The diagrams show what happens when…

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A summary
The table summarises the main types of electromagnetic radiation and a typical use
for each of them.

Gamma radiation
Gamma waves have a very high frequency. Gamma radiation cannot be seen or
felt. It mostly passes through skin and soft tissue, but some of it is absorbed by…

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reduce the amount of ultraviolet radiation that reaches deeper skin tissues. Darker
skins absorb more ultraviolet light, so less ultraviolet radiation reaches the deeper
tissues. This is important because ultraviolet radiation can cause normal cells to
become cancerous.
Ultraviolet radiation is used in:
Sun beds
Security pens
Fluorescent lights (coatings…

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The speed of a comet increases as it gets closest to the sun, and is greatest when
the comet is nearest to the sun. Comets are often visible from Earth when they get
close to the sun, because the sun's heat vaporises material from the surface to form
a tail.…

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The distances involved are huge: the distance from one star and another in a galaxy
is millions of times more than the distance between the planets in the solar system.
Meanwhile, the distance from one galaxy to another is millions of times more than
the distance between the stars in…

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An optical fibre is a thin rod of highquality glass. Very little light is absorbed by the
glass. Light getting in at one end undergoes repeated total internal reflection, even
when the fibre is bent, and emerges at the other end.

Information such as computer data and telephone calls can…

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Analogue signals
Noise adds extra random information to analogue signals. Each time the signal is
amplified the noise is also amplified. Gradually, the signal becomes less and less
like the original signal. Eventually, it may be impossible to make out the music in a
radio broadcast against the background noise,…


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