# Physics (p1)

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## THE SOLAR SYSTEM

many early people thought the sun and all the plannets moved around earth.

changing ideas

Greek astronomer called Ptolemy published a geocentric (meaning the earth in the centre) model, this tried to explain the motions of the plannets.

in 1543 Nicilaus copernicus published a book that argued that earth and the plannets where in orbits around the sun. this is called the heliocentric (meaning the sun is in  the centre) model.

ways of observing the universe using light waves

• we can only see some stars and planets using the naked eye.
• telescopes allow us to see more distant and fainter objects.
• photographs provide a record of observations that can be studied later or analysed by computer.
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## GALILEO

Galileo Galilei was the first astronomer to make observations using telescopes.

In 1610 he reported that he had observed four moons orbiting jupiter.

These were the first objects seen to be orbiting around something that was not earth.

This observation supported the heliocentric model idea.

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## REFLECTION AND REFRACTION

Light travels as waves, normally in straight lines unless it is reflected or refracted.

• reflection is when light bounces off a boundry between different materials.
• refraction is when light passes from one material to anoter

here is a labelled diagram explaining why waves change direction when they pass from air to water.

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## LENSES

Lenses are specially shaped pieces of transparent material that change the direction of light rays. A converging lens makes rays of light come togerther.

• the point at which the parallel rays are brought together is called the focal point. The distance between the lense and the focal point is called the focal length.
• The fatter the lens the shorter the focal point.
• The magnification of the image depends on the focal length and the distance between the object and the lens.
• A converging lens can be used as a magnifying glass if it is hld close to an object.

Finding the focal length

The focal length is the distance between the lens and the paper.

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## TELESCOPES

Simple Telescope

The first telscopes used lenses to gather more light and to magnify the image.

A refracting telescope uses two converging lenses.

The objective lens brings rays of light from a distant object to a point to form an image.

The eyepiece lens acts as a magnifying glass and magnifies this image.

Reflecting Telescope

A reflecting telescope uses a curved mirror to gather light from distant objects and a converging lens as an eyepiece to magnify the image. If a telescope needs to see very dim objects, it is easier to make a very large mirror than a very large lens. reflecting telescopes give better guality images than reflecting telescopes of similar sizes.

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