GCSE PHYSICS - What is Light? - What is the Speed of Light? - What is a Light Year?

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What is Light?

Light is a transverse wave.
It is one part (region) of the electromagnetic spectrum.
Light is the visible region, it is the part used by our eyes to see.
Like any electromagnetic wave, light can travel through a vacuum.
Light travels through the vacuum of space from the Sun to the Earth.

What is the Speed of Light?

Light travels very quickly. There is nothing that can travel faster.
The speed of light is 300,000,000 m/s in air
(that is 300 million metres per second - not easy to imagine!).
The speed of sound in air is approximately 330 m/s,
so light is almost one million times as fast.

You can sometimes notice that light is travelling faster than sound.
In a storm, the light and the sound are generated at the same time
but you see the lightning flash before you hear the sound.
The light has travelled to your eyes more quickly than
the sound has travelled to your ears from the same origin.

What is a light year?

In one year, light has travelled ten thousand billion kilometres.
This very large distance is called a light year
and is used by astronomers to measure
the vast distances between stars and galaxies.

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