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Topic 1 Visible light and the Solar System
The ancient Greeks made detailed measurements of the movements of objects in the sky. Ptolemy used
these measurements to explain how the Sun, the Moon and the planets moved in orbits and his idea put the
Earth in the centre of everything a geocentric model.
On the other hand, the Polish astronomer Nicolaus Copernicus thought that Ptolemy's measurements fitted a
different model, that of the heliocentric model. However, the Church didn't like the idea of the sun being the
centre of the solar system so put an introduction into Copernicus' book before it was published saying that
the book contained ideas with no proof.
At the end of the 16thcentury the telescope was invented which allowed scientists to see objects in space in
much greater detail than with the naked eyes and to find new objects.
Galileo used the telescope which helped him discover four of Jupiter's moons, all of which orbited Jupiter and
not the earth. This and other observations led him to support Copernicus' idea. However, the Church was still
against the idea and kept Galileo under house arrest for the last ten years of his life.
With the improvement of telescopes, new planets were discovered such as Uranus, Neptune and dwarf
Luminous objects in space give out visible light that travels as waves of energy. These visible light waves
allow people to study distant objects.
The invention of photography has allowed astronomers to make more detailed observations instead of
having to paint what they see in the telescope.
Many objects give out other types of energy-carrying waves like radio and microwaves. Today, there are
telescopes that can detect different types of these waves and this new data helps scientists make
conclusions about the universe.
When a wave hits a boundary between one medium and another some of its energy is reflected.
The angle of reflection = angle of incidence.
The light is reflected because of the change in density. Whenever a wave reaches a medium with a different
density some of the wave is reflected at the boundary.
Waves travel at different speeds in substances which have different densities. EM travel more slowly in
denser material while sound waves travel faster in denser substances.
When a wave crosses a boundary between two substances it changes speed.
If the wave hits the boundary `face on' it slows down but carries on in the same direction.
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When light shines on a glass window pane, some of the light is reflected but a lot of it passes through the
glass and gets refracted as it does so. This is what happens:
o As light passes from air to glass, it slows down. This causes the light ray to bend towards the normal.
o When light reaches the air again, it is passing through a less dense medium. This means it gets faster
and bends way from the normal.…read more
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Some images can be shown on a screen, which is what Galileo most likely did so he could draw the image. This
is image is a real image as it's an image in which the rays of light actually meet at the point where the image is
Virtual images however, are different. In a virtual image the rays of light appear to come from an image but
do not actually from that image. A virtual image cannot be shown on a screen.…read more
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Water particles just move up and down as wave passes- they aren't carried to the shore. Waves in which
particles move at right angles to the direction that the wave is going are called transverse waves.
Waves only transfer energy and information without transferring matter.
Most waves are transverse:
o Light and all other electromagnetic waves.
o Waves on strings and springs.
o Ripples on water.
The vibrations are at 90 to the direction of travel of the wave.…read more