O Level Physics

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The Solar System is about 4,600
million years old. It was formed
from a nebula – an enormous
cloud of dust and gas created
when a dying star exploded.
Over millions of years, the temperature rose and the globule
became more compressed, causing it to start spinning.
How was the Solar System formed?
When shockwaves from other
dying stars hit the nebula, it
collapsed and formed a globule.
The force of the spinning shaped the globule into a central
core surrounded by a disk of gas and dust. Eventually, the
core became the Sun and the material in the disk formed
the planets and asteroids of the Solar System.

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Which of these objects are
light sources?
The Solar System is made up
of various celestial objects:
 the Sun
 the planets
 moons
 asteroids
 comets.
The Sun is a star and a light source. It is a massive ball of
hot glowing gas, which gives out huge amounts of heat and
light energy.
What makes up the Solar System?

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The Sun is the star at the centre
of the Solar System, about 150
million kilometres from Earth.
Scientists used to think that chemical reactions powered the
Sun, but this could not explain how it had managed to stay
‘burning’ for millions of years.
What is the Sun?
The Sun mostly consists of
hydrogen and helium.
Its mass accounts for more
than 99% of the total mass of
the Solar System.
It is now known that nuclear fusion is the process that
releases the Sun’s energy.

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The planets travel around the Sun in near-circular orbits.
Comets are celestial objects that also travel around the Sun,
but in very elliptical orbits.
The head of a comet is a lump of
ice and dust, a few kilometres in
diameter.
What are comets?
The tail consists of gas and dust
that are released from the comet
by the heat of the Sun.
For most of its orbit, a comet is a
long way from the Sun. The tail of
the comet only appears when the
its orbit passes nearest the Sun.

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The Solar System – true or false?

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A star is ‘powered’ by nuclear fusion
reactions taking place in its core.
In the Sun and most stars, hydrogen atoms fuse together
to form helium. This provides the energy for life on Earth.
What powers a star?
It would take 2,000 million nuclear power plants a whole
year to produce the same amount of energy on Earth.
This process releases huge amounts of
energy. Each second, the Sun produces
400,000,000,000,000,000,000,000,000 watts of energy!
Nuclear fusion involves light atomic
nuclei joining together (fusing) to form
heavier ones.

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Using nuclear fusion

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However, not all elements are made in the early stages of
a star’s life. Some of the heavier elements are only made
when a star explodes at the end of its life.
Nuclear fusion in stars produces
new atoms.
How are elements made?
When all the hydrogen has been
used up, other elements are fused
together to make the heavier
elements of the periodic table.
In the early stages of a star’s
life, light elements such as
helium are mainly formed.

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How do stars begin and end?

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A white dwarf is formed
at the end of the life cycle
of a star that is about the
same size as the Sun.
What is a white dwarf?
This photograph was
taken with the Hubble
Space Telescope and
shows ancient white
dwarf stars in the Milky
Way galaxy.
The white dwarf stars are
shown ringed in blue.

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What is a supernova?

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After a really massive red giant collapses in a supernova
explosion, it leaves an object so dense that nothing, not
even light, can escape its gravitational pull.
Some scientists believe
that there are black holes
at the centre of galaxies.
If light cannot escape from
a black hole, then how can
a black hole be observed?
How are black holes formed?
The end of the life cycle of really massive stars is different
to that of massive stars.
This is called a black hole.

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How can a black hole be ‘seen’?

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Lifecycle of small stars

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Lifecycle of large stars

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1. What two elements make up most of the Sun?
hydrogen and helium
Questions about stars
the Sun  red giant  white dwarf
5. What is the fate of a star similar to the Sun?
A huge cloud of gas and dust from which a star is
born.
2. What is a nebula?
nuclear fusion
3. What process has allowed the Sun to emit light and heat
energy over thousands of million of years?
neutron star
4. Which is the most dense, a white dwarf or a neutron star?

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Terms about the lifecycle of stars

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To find the Sun, you would have to shrink
down to stand on the piece of dust.
When thinking about the Universe, it can be difficult
to understand the size and scale that is involved.
How big is the Universe?
One way to think about this is to imagine
the known Universe scaled down to the
size of planet Earth.
Our galaxy would be equivalent to the
size of just one micron – that’s roughly
the same size as a small piece of dust!
It would then be like finding one particular grain of sand
in a seven-metre-wide circular pool filled with sand!
And this is just the known Universe…

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Journey through the Universe

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Size in the Universe

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Terms about the Universe

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Identify the celestial objects

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Is the Universe expanding?

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Scientists examining the light
emitted by stars observe dark
lines in the spectrum.
What is red shift?
This red shift suggests that distant galaxies are moving away
from Earth and supports the idea of an expanding Universe.
Edwin Hubble observed that the pattern of dark lines in
light from distant galaxies is shifted towards the red end
of the spectrum.
These dark lines are caused by
different elements, such helium,
in the stars being studied.
Red shift occurs because of the Doppler effect, which can
be observed in sound waves and electromagnetic waves.

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What is the Doppler effect?

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The Doppler effect means that sound
moving away from an observer appears
to be lower in frequency.
It has also been observed that the further away a galaxy is,
the greater the amount of red shift.
How does the Doppler effect work in space?
This means the distant galaxies must be
moving away from the Earth.
The same thing happens with light from
distant galaxies, which appears to be
shifted towards the low frequency, red
end of the spectrum.
This means that very distant galaxies must be moving faster
than near, all of which is evidence for the Big Bang theory.

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What is the Big Bang theory?
The observation of red shift is a key piece of evidence for the
Big Bang theory about the origin of the Universe.
The other key piece of evidence for
the Big Bang theory is cosmic
microwave background
radiation (CMB).
This states that the Universe ‘began’ with a colossal explosion
13,700 million years ago and has been expanding ever since.
CMB is radiation remaining
from the Big Bang explosion
and fills the whole of the Universe.
This radiation has cooled as the Universe has expanded and
is now slightly less than 3 degrees above absolute zero.

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The Universe from beginning to end

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 black hole – An object whose gravitational pull is so strong
that nothing can escape, not even light. It is formed after a
really massive star collapses in a supernova.
 comet – A lump of rock and ice, which has a very elliptical
orbit around the Sun.
 Doppler effect – The shift in frequency of a sound wave
or an electromagnetic wave due to the relative movement of
the source or observer.
 galaxy – A vast collection of millions of stars.
 nebula – A massive cloud of gas and dust in which a star
is formed.
 neutron star – The very dense core that remains after a
massive red giant collapses in a supernova.
Glossary (1/2)

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 nuclear fusion – The process in which lighter atomic
nuclei join together to make heavier atomic nuclei and a
massive amount of energy is released.
 red giant – The huge red star formed when a star
expands and shines less brightly as it starts to die.
 red shift – A shift in the wavelength of light towards the
red end of the spectrum. It occurs when the light source is
moving away from the observer and is evidence for an
expanding Universe.
 supernova – The huge explosion that occurs when a
massive red giant is at the end of its life.
 white dwarf – The core that remains after the outer
layers of a small red giant drift away.
Glossary (2/2)

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Anagrams

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Multiple-choice quiz