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Further Physics

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Title: Further Physics


1
Further Physics
Studying the Universe
M Barker Shirebrook Academy
2
P7.1 Naked Eye Astronomy
3
The Nine(?) planets of our Solar System
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Which planets can be seen with the naked eye?
4
The Earth orbits the sun
every year (365 1/4 days)
5
The Spin of the Earth
The Earth rotates on its axis every 24 hours
Whats wrong with this picture?
6
The Spin of the Earth
Because of this spin the sun and stars appear to
move across the sky in an east-west direction
The sun takes 24 hours, the stars take slightly
less than this and the moon takes longer!
7
Solar days vs Sidereal days
Basically, a solar day is the normal 24 hours.
However, the Earth actually spins in 23 hours 56
minutes. This period of time is called a
Sidereal day. Heres why
After one day the Earth is in a different
position and so the sun and stars will appear
in the same place after 23 hours 56 mins, not 24
hours.
8
The Earth and the Moon
The moon appears to move east-west across the sky
in 24 hours 49 minutes. This is because the moon
moves around during the course of 24 hours
  1. After 24 hours the Earth has rotated once but the
    moon has moved on
  2. Therefore the Earth needs to rotate for another
    49 minutes for the moon to appear in the same
    place

9
Phases of the moon
Appearance
10
Appearance
11
Appearance
12
Eclipses
Solar eclipses occur when the moon is between the
sun and the Earth
13
Eclipses
The moon takes a _____ to orbit the Earth.
However, solar eclipses do not occur every month
because the moons orbit is inclined at 5O to
that of the ______. Eclipses only occur when the
moon passes through the _____ the apparent path
the ____ traces out across the _____.
Words sky, sun, month, ecliptic, Earth
14
Eclipses
Lunar eclipses occur when the Earth is between
the sun and the moon
During a lunar eclipse the moon might look like
this
15
Viewing stars
The stars we see in the summer and in the winter
should be different
Stars in the summer
Stars in the winter
16
Viewing Planets
The position of Venus changes in a different way
to the stars behind it (retrograde motion).
This was the first evidence that planets orbit
the sun
17
Viewing stars
18
P7.2 Light, Telescopes and Images
19
Refraction
20
Refraction through a glass block
Light slows down but is not bent, due to entering
along the normal
21
Lenses
Lenses use the idea of refraction
22
Converging and diverging lenses
CONVERGING (Convex) Thickest at the centre
DIVERGING (Concave) Thinnest at the centre
23
Ray Diagrams for Lenses
The rays of light are refracted INWARDS and meet
at the focus, F. The image formed is REAL in
other words, it can be seen on a screen
F
The rays of light are refracted OUTWARDS. A
VIRTUAL image is formed in other words, the
image doesnt actually exist
F
24
Ray diagrams
To draw ray diagrams follow these three rules
1) Draw a ray from the TOP of the object
PARALLEL to the axis and then going through F
F
F
2) Draw a ray from the TOP of the object going
through the CENTRE of the lens (which will be
undeviated)
3) Draw a ray from the top of the object through
F to the left of the lens and parallel to the axis
25
Ray diagrams 2
If the object is below the axis follow this step
4) Draw a ray from the bottom of the object
parallel to the axis and then up through the
focal point
F
F
26
F
F
27
F
F
28
F
F
29
F
F
30
F
F
31
More about lenses
Compare thin and thick lenses
Lenses are measured in units called dioptres
where converging lenses (for long sighted
people) have positive values and diverging lenses
(for short sighted people) have negative values.
32
Lenses in Telescopes
Because stars are very far away, the rays of
light from them enter a telescope effectively
parallel
Notice that this telescope has two converging
lenses. The more powerful one is the eyepiece
lens.
33
Using Concave Mirrors
Notice that concave mirrors can be used to focus
light
F
Concave mirror
34
Mirrors in Telescopes
Astronomical telescopes tend to use large concave
mirrors as well as a convex lens. This allows
them to collect more light and the bigger the
telescope, the more light they collect
35
Magnification
Basically, magnification means how much bigger
the object looks
  • Example questions
  • What is the magnification of a telescope with an
    objective lens focal length of 15m and a eyepiece
    focal length 3m?
  • A telescope has a 100x magnification. If the
    focal length of the eyepiece is 50cm what is the
    focal length of the objective lens?

36
Diffraction
06/01/2016
Diffraction is an effect seen when a wave travels
around a corner or through a narrow gap
More diffraction if the size of the gap is
similar to the wavelength
More diffraction if wavelength is increased (or
frequency decreased)
37
Diffraction in Telescopes
The hole at the end of a telescope is called an
aperture. To avoid problems caused by
diffraction through this aperture, the size of
the hole must be much larger than the wavelength
of the radiation it is observing.
38
Spectra
Recall that spectra can be produced by the
refraction of light through a prism
A spectrum can also be produced by the
diffraction of light through a diffraction
grating (basically a set of very small gaps)
39
P7.3 Mapping the Universe
40
Distances in space
41
Parallax
Parallax uses the idea that, as the Earth moves
around the sun, the apparent position of nearby
stars changes in relation to distant stars behind
it
Stars that are further away from the Earth will
have a smaller parallax angle.
42
Using parallax
Astronomers often use the parsec to describe
galactic distances. A parsec is roughly 3¼ light
years.
Angles involved in parallax measurements are
often very small and are measured in seconds of
an arc (arcseconds). A second of an arc is
1/60th of a minute of an arc, which is 1/60th of
a degree. In other words, one arcsecond
1/3600th of a degree. A parsec is defined as the
distance to a star with a parallax angle of one
arcsecond.
The approximate distance to a star can be
calculated using this formula
  1. Proxima Centauri has a parallax angle of 0.77
    arcseconds. How far away is it in parsecs?
  2. The nearest galaxy, Andromeda, is 0.77Mpc away.
    What would the parallax angle be in arcseconds?

43
Luminosity
06/01/2016
Luminosity means how bright the star is. The
luminosity of a star depends on its size and
temperature.
44
Measuring distance using brightness
The sun looks very bright. But, to be fair, its
very close to us so it should look bright!
45
Measuring distance using brightness
When I look at these stars some appear brighter
than others. This because they are either
brighter stars or closer to me. For example, the
star Antares is 10,000 times brighter than the
sun but it is 500 light years away from me, so it
is only the 15th brightest star in the night sky.
There are also Cepheid variable stars, which
vary in brightness. Astronomers use the
frequency of its pulsing to work out how bright
it is and how far away it is.
46
Cepheid Variable Stars
A Cepheid Variable star is one whose magnitude
varies over time
The period is related to their luminosity.
You can measure the distance of these stars
by 1) Observe for a few weeks to find the
period 2) Use various mathematical relationships
to determine the distance
Measurements of the distances to Cepheid variable
stars shows that they are very far away and must
be outside of our galaxy!
47
The Milky Way
OUR SUN is one of millions of stars that orbit
the centre of the Milky Way
Scientists realised that the Milky Way contains
millions of stars only after the invention of
telescopes. Telescopes also helped scientists
discover fuzzy objects and these were
originally called nebulae.
48
The Curtis-Shapley debate, 1920
After observing nebulae I said that the universe
consisted of many galaxies.
I disagreed and said that the universe contained
only one big galaxy the Milky Way, and this
galaxy contained the nebulae.
I settled the debate by observing Cepheid
Variable stars and found that they were much
further away than our own galaxy.
49
Hubbles Law
Astronomers have observed Red Shift and Cepheid
variable stars in lots of galaxies and deduced
the fact that more distant galaxies are moving
faster than closer ones
50
Hubbles Law
Using this evidence I concluded two things that
the universe is expanding AND the recession
velocity is proportional to the galaxys distance
from us, therefore
V Hd
where H Hubbles Constant (21 x 10-18 s-1)
(or H can be measured in kms-1Mpc-1 and distance
is in Mpc)
51
Questions on Hubbles Law
  1. A galaxy is 5x1020km from Earth. If Hubbles
    constant is 2x10-18s-1 calculate how fast that
    galaxy is moving.
  2. Another galaxy is 10Mpc from Earth. Taking H to
    be 75kms-1Mpc-1 calculate its recessional
    velocity.
  3. Another galaxy has a recessional velocity of
    500km/s. Calculate the distance to the galaxy in
    both megaparsecs and kilometres (take H to be
    2x10-18s-1).

52
The Big Bang Theory
06/01/2016
The motion of galaxies, as observed with
telescopes, indicates that galaxies are all
moving away from each other. In other words, the
universe is expanding. What happened to start
this off around 14 billion years ago?
53
(No Transcript)
54
P7.4 The Sun, the stars and their surroundings
55
Wavelength and Energy Output
06/01/2016
All stars give out lots of different wavelengths
of radiation
T6000K
When wavelength goes up (and frequency goes down)
what happens to the stars intensity and
temperature?
56
Ionisation revised
06/01/2016
Radiation is dangerous because it ionises atoms
in other words, it turns them into ions by
knocking off electrons
57
Spectra introduction
06/01/2016
58
06/01/2016
Spectra
59
Absorption Spectra
06/01/2016
Some wavelengths of light are absorbed by the gas
an absorption spectrum.
60
Spectra
06/01/2016
61
Emission Spectra
06/01/2016
62
Spectra
06/01/2016
Consider a ball in a hole
When the ball is here it has its lowest
gravitational potential energy.
We can give it potential energy by lifting it up
If it falls down again it will lose this gpe
63
Spectra
06/01/2016
By looking at the spectra from stars we can work
out what gases are inside it. This is how we
know the sun is made of hydrogen.
64
An Example Question
06/01/2016
Here are the emission lines for hydrogen and
helium
Which gas is in this star?
65
Particle Motion in Gases
Gas pressure is caused by particles hitting the
side of a container. Anything we do that
increases those collisions will increase the
pressure
66
Particle Motion in Gases
Consider decreasing the volume
The particles should collide with the sides of
the container _____ often, therefore the pressure
is ________.
67
Particle Motion in Gases
Now consider increasing the temperature as well
The particles should collide with the sides of
the container _____ often, therefore the pressure
is ________. This could cause the container to
______.
68
Pressure and Temperature in gases
P
T
69
Pressure and Temperature in gases
P
T
-2730C
The Kelvin temperature scale starts at 0K (
-273OC). To convert degrees centigrade into
Kelvin simply add 273.
70
Absolute Temperature
  • Absolute Temperature starts at 0K and
    represents the temperature at which particles
    have zero kinetic energy. It goes up in the same
    steps as OC. For example
  • The freezing point of water is 273K
  • The boiling point of water is 373K
  • Room temperature is around 293K

71
Volume and Temperature in Gases
For a constant mass of gas at fixed pressure, the
volume occupied by the gas is proportional to its
absolute temperature.
72
Volume and Temperature in Gases
Provided the pressure of a gas stays the same we
can use this relationship to calculate the volume
of a gas
  1. A gas changes in temperature from 200K to 300K.
    If its original volume was 2m3 what is the new
    volume?
  2. Another gas is halved in volume. What will
    happen to its temperature?
  3. A third gas is kept at constant pressure while
    being compressed from 20 litres to 15 litres. If
    its new temperature is 275K what was its original
    temperature?

3m3
It will halve
367K
73
Boyles Law
For a fixed mass of gas at constant temperature
(isothermal), pressure is proportional to
1/volume.
Higher temperature?
Lets draw this




74
Pressure and Volume in gases
This can be expressed using the equation
Initial Pressure x Initial Volume Final Press.
x Final Vol. PIVI PFVF
  1. A gas has a volume of 3m3 at a pressure of
    20N/m2. What will the pressure be if the volume
    is reduced to 1.5m3?
  2. A gas increases in volume from 10m3 to 50m3. If
    the initial pressure was 10,000N/m2 what is the
    new pressure?
  3. A gas decreases in pressure from 100,000 Pascals
    to 50,000 Pascals. The final volume was 3m3.
    What was the initial volume?
  4. The pressure of a gas changes from 100N/m2 to
    20N/m2. What is the ratio for volume change?

40N/m2
20KN/m2
1.5m3
15
75
The Gas Equation
A while ago we said that Pressure x Volume
Constant (Boyles Law)
also, we just said pressure is proportional to
temperature (Pressure law) and we said volume
is proportional to temperature (Charles Law)
Combining these three equations gives
76
Some example questions
  1. An ideal gas has a volume of 2m3 and a pressure
    of 101KPa (101,000 N/m2) at a temperature of
    300K. The gas is then increased in temperature
    to 400K but kept at constant volume. Calculate
    the new pressure.
  2. The same gas is then allowed to cool to 200K
    while being kept at constant pressure. Calculate
    the new volume.
  3. Another gas at 300K and 101KPa is allowed to
    halve in volume while being kept at the same
    pressure. What is the new temperature?

135KPa
1m3
150K
77
The Life Cycle of a Star
78
Stage 1 Nebulae
A nebulae is a collection of dust, gas and
rock. Some examples of nebulae
79
Dark nebula
80
Emission nebula
81
Planetary nebula
82
Reflection nebula
83
Stage 2 Protostar
84
Stage 3 Main Sequence
85
Nuclear Fusion in stars
06/01/2016
06/01/2016
Proton
Neutron
Nuclear fusion happens in stars but its not
possible to use it in power stations yet as it
needs temperatures of around 10,000,000OC
86
Fusion Reactions
06/01/2016
When the temperature of the star increases
nuclear fusion reactions will start. Heres the
equation
  1. What are ß particles and why are they emitted?
  2. Why is energy released in this reaction?

87
Energy-mass equivalence
In every fusion (or fission) reaction a little
bit of mass is lost. This mass turns into
energy and you can use my famous equation to work
out how much
Emc2
where E the energy released, m the mass
converted into energy and c the speed of light.
88
The Structure of our Sun
The hotter a star is, the higher peak wavelength
it emits (e.g. blue stars are hotter than red
stars).
89
The Hertzsprung-Russell Diagram
06/01/2016
Supergiants
L (relative to our sun)
T (K)
90
Stage 4 Red Giant
Eventually the hydrogen and helium will run out
and the star will leave the main sequence. When
this happens the star will become colder and
redder and start to swell
In red giants and supergiants, nuclei such as
oxygen and nitrogen are formed.
91
Stage 5 The Death
What happens at this point depends on the size of
the star 1) For SMALL stars the red giant will
collapse under its own gravity and form a very
dense white dwarf, where no fusion reactions will
take place
92
2) If the star was a RED SUPERGIANT it will
shrink and then EXPLODE, releasing massive
amounts of energy, dust and gas.
This explosion is called a SUPERNOVA. Heavier
nuclei such as iron could be made in the core
prior to the supernova.
93
The dust and gas on the outside of the supernova
are thrown away by the explosion and the
remaining core turns into a NEUTRON STAR.
If the star is big enough it could become a BLACK
HOLE.
94
Life on Other Planets
06/01/2016
Research task
Is it likely that other planets in our solar
system could have life? Explain your
answer. Extend your inquiry to other solar
systems what criteria must be met in order for
a planet to potentially have life on it?
95
Searching for Aliens
06/01/2016
Humans have been searching for me for over 50
years. Do you think I exist?
Quite possibly, We know that hundreds of
nearby stars have planets around them and we
also know that there are billions of stars in the
universe so surely one of these planets has life
96
P7.5 The Astronomy Community
97
Observing the Universe
98
Observing the Universe
Consider different types of telescope
What are the advantages and disadvantages of each?
99
Common sites for Ground-Based telescopes
What advantages do these sites offer?
100
Using Computers with Telescopes
Telescopes like this one are often controlled by
computers.
What advantages does this offer?
  1. The telescope can be controlled remotely
  2. It can track objects continuously
  3. Its more precise
  4. The computer can record and process the data

101
Benefits of observing above the atmosphere
  • Clearly, ground-based telescopes are a problem
    because of a number of things
  • The amount of light absorbed by the atmosphere
  • Bad weather
  • Light is refracted, diffracted and scattered by
    the atmosphere (causing stars to twinkle)
  • Light pollution from nearby cities
  • The solution is to put telescopes in space or
    build them high up on a mountain. Here are two
    examples of space-based telescopes

102
Hubble Space Telescope (HST)
  • Launched in 1990, due to finish operating in
    2010
  • Takes images in the visible light, ultra-violet
    and near infra red regions
  • Orbits the Earth every 97 minutes

103
Infra Red Astronomical Satellite (IRAS)
  • Surveys infra red patterns in space
  • Launched in 1983 and operated for 11 months
  • The number of known astronomical bodies was
    increased by 70 due to infra red observations

104
International Collaboration
Heres the International Space Station, a joint
project by NASA, the Russian Space Agency, the
European Space Agency, the Japan Aerospace
Exploration Agency and the Canadian Space Agency
  • What advantages does international collaboration
    bring in terms of
  • Cost?
  • Pooling of expertise?

105
Building Observatories
What factors are involved in planning, building
and closing down a large observatory?
  • Cost
  • Environmental impact
  • Social impact
  • Working conditions
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