# Physics 6 markers

• Created by: Faolan
• Created on: 10-06-15 17:28

## Proving the law of reflection

• With a sharp pencil and a ruler, draw a straight line AOB on a sheet of white paper using a ruler
• Use a protractor to draw a normal, N, at point O
• With the protractor draw straight lines at various angles to the normal ranging from 15 degrees to 75 degrees
• Place a plane mirror on the paper so that is back rests on the line AOB
• Using a ray box, shine a ray of light along the line marked 15 degrees
• Mark two crosses on the reflected ray on the paper
• Remove the mirror, use a ruler to join the crosses on the paper with a pencil, and a extend the line backwards to point 0- this line shows the reflected ray
• Measure the angle of reflection with a protractor
• Record in a table the angles of incidence and reflection
• Repeat the experiment for different angles of incidence up to 75 degrees
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## The image in a plane mirror.

• Supports a plane mirror vertically on a sheet of white paper, and with a pencil draw straight lines at the back to mark the position of the reflecting surface.
• Use ray box to direct two rays of light form point O towards points A and B on the mirror
•   Mark the position of the O with a using a pencil.
• Mark two crosses on each of the real reflected ray.
•  Remove both the ray box and the mirror
• Using a ruler join the crosses with a pencil line so as to obtain the paths of the real form A to B
• Extend these lights behind the mirror – they meet at I, the point where the image is formed
• Measure the distance from the image I to the mirror line (IN) and the distance form the object 0 to the mirror line- they should be the same
•  Repeat the experiment for different positions of the objects
• In each case the object 0 and its image I should be the same perpendicular distance form the mirror
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## Measuring the angles of incidence and refraction

• Þ   Place the glass block on a sheet of white paper and draw around its out line with a sharp pencil
• Remove the block and draw a normal near the middle of one of the longer sides
•  Use a protractor to draw a line representing an incident ray at an angle of 40 degrees
• Replace the block on its outline on the paper
• Place the ray box to direct a ray of light along the line drawn
• Mark the path of the emergent ray
•  Remove the block and join the points of incidence and emergence with a straight line to construct the path of the ray through the block
•  Repeat this procedure for angles of incidence of 50 degree etc. using the normal line
• Record results in a table
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## Star description

• Most stars are composed mainly of hydrogen and helium. The hydrogen gas at a stars centre exists in the form of nuclei not atoms or molecules.
• These nuclei are positively charged and therefore tend to repel each other.
• The temperature at the centre of a typical star is very high (more than 15 million degrees) so the hydrogen nuclei are moving at enormous speeds.
• When they collide they can from a new heavier nucleus (helium) this is nuclear fusion and it causes the release of vast quantities of energy.
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## How are stars formed

• A star is formed from clouds of hydrogen and dust, known as a stellar nebulas
• Particles of hydrogen come together because of gravity
• These clouds become more and more dense as the particles get closer and closer together
• Hydrogen particles start to spiral inwards and the temperatures rises enormously
• The temperature reaches about 15 million degrees
• At this temperature nuclear fusion begins and  star is born (This is how is was born)
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## How are planets formed

• The remaining clouds of gas and dust are called a planetary nebula
• They clump together due to gravity in a process called accretion
• Over a very long period of time they become planets
• The presence of a massive star may cause them to be trapped by its orbit.
• Since then gas and dust clouds originally spiralled in the same direction so the planets would orbit that star in the same sense and in the same place
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## 6 marker

Why are the four inner planets rocky and the four outer planets gaseous?

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• As the sun began to shine, its radiation “blew” much of the gas away to the outer reaches of the solar system.
• Here the gas collected by gravitation to form the outer planets.
• However, the dust particles, being of greater mass, were not “blown not so far and over millions of years, gravitational accretion caused the dust too form the inner rocky planets
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## What is solar solubility

• The sun is covering mass into energy at a rate of about 4 million tonnes per second
• But its apparent size in the sky has remained the same for as long as humankind has been on earth
• This is because the force f gravity which pulls inwards the centre of exactly balances the outward force due to thermonuclear explosions.
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## Explain the big bang theory

• Most physicists today accept the BIG BANG THEORY as the best model o describes the origin of the universe.
•   The big bang theory occurred between 12000 and 15000 years ago from a tiny point that physicist’s call a singularity. It was not an explosion off the conventional type, because it was only then that matter, energy and time came into existence.
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## Explain the big bang theory

• Most physicists today accept the BIG BANG THEORY as the best model o describes the origin of the universe.
•   The big bang theory occurred between 12000 and 15000 years ago from a tiny point that physicist’s call a singularity. It was not an explosion off the conventional type, because it was only then that matter, energy and time came into existence.
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