Transcript Unit P1 - Universal Physics 1

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Unit 1 – Universal Physics
(EdExcel)
N Smith
St. Aidan’s
Topic 1 – Visible Light and the
Solar System
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Our understanding of the universe
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Up until the 16th Century people believed that
the Earth was the centre of the universe – this
is called the “Geocentric model” and I made a
model of the universe based on it.
Ptolemy, AD 90-168
I published my “On the revolutions of the
celestial spheres” just before my death and
showed that the Earth and other planets orbit
around the sun – the “Heliocentric model”.
Copernicus, 1473-1543
Evidence for the Heliocentric Model
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I helped develop the modern telescope
and made measurements with it that
proved that the Copernican model of
the solar system was correct.
Galileo, 1564-1642
Jupiter and its moons, as seen
through a telescope
The orbits of
these moons
Observing the Universe
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What are the
advantages and
disadvantages of
each of these
methods?
A complex
digital
camera will
be in here
An introduction to Waves
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A Wave is a “movement of energy” but NOT a transfer of
matter
Wave definitions…
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1) Amplitude – this is
“how high” the wave
is:
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
4) Speed – this is how fast the wave travels and is
measured in metres per second (m/s)
Transverse vs. longitudinal waves
Transverse waves
are when the
displacement is at
right angles to the
direction of the
wave.
Displacement
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Direction
Examples – light, other EM waves, some seismic waves
Displacement
Direction
Longitudinal waves
are when the
displacement is
parallel to the
direction of the
wave…
Examples – sound, some seismic waves
Refraction through a glass block:
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Wave slows down and bends
towards the normal due to
entering a more dense medium
Wave slows down but is
not bent, due to entering
along the normal
Wave speeds up and bends
away from the normal due to
entering a less dense medium
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Refraction
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Refraction is when waves ____ __ or slow down due to
travelling in a different _________. A medium is
something that waves will travel through. When a pen is
placed in water it looks like this:
In this case the light rays are slowed down by the water
and are _____, causing the pen to look odd. The two
mediums in this example are ______ and _______.
Words – speed up, water, air, bent, medium
Lenses
Lenses use the idea of refraction:
When light enters a
MORE DENSE medium
it slows down…
A prism uses this idea
to split light. This
happens because purple
light is refracted more
than red light
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Another example:
The lens in the eye is used to focus what we see:
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Converging and diverging lenses
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CONVERGING (Convex)
Thickest at the centre
DIVERGING (Concave)
Thinnest at the centre
Ray diagrams for lenses 1
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A “distant
object”
Focal length
The rays of light are
refracted INWARDS and
meet at the focus, F.
F
F
The image formed is REAL –
in other words, it can be
seen on a screen
The rays of light are
refracted OUTWARDS.
A VIRTUAL image is formed
– in other words, the image
doesn’t actually exist
Lenses in Telescopes
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Because stars are very far away, the rays of light from them
enter a telescope effectively parallel:
Objective lens
(convex)
Focal point
Eyepiece
lens
The objective lens basically gathers as much light as possible
from the distant star and focuses it inside the telescope. The
eyepiece lens then magnifies this image into the eye.
Mirrors in Telescopes
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Astronomical telescopes tend to use large concave mirrors as
well as a convex lens. This allows them to collect more light:
Eyepiece
lens
Objective lens
(convex)
Flat mirror
Concave
mirror
The Wave Equation
All E-M waves obey the Wave Equation:
Wave speed (v) = frequency (f) x wavelength ()
in m/s
in Hz
in m
V
f

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Some example wave equation questions
1) A water wave has a frequency of 2Hz and a wavelength
of 0.3m. How fast is it moving?
0.6m/s
2) A water wave travels through a pond with a speed of
1m/s and a frequency of 5Hz. What is the wavelength
of the waves?
0.2m
3) The speed of sound is 330m/s (in air). When Dave
hears this sound his ear vibrates 660 times a second.
What was the wavelength of the sound?
0.5m
4) Purple light has a wavelength of around 6x10-7m and a
frequency of 5x1014Hz. What is the speed of purple
light?
3x108m/s
Distance, Speed
and Time for waves
Speed = distance (in metres)
time (in seconds)
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D
S
T
1) A water wave travels 200 metres in 40 seconds. What is its speed?
2) Another wave covers 2km in 1,000 seconds. What is its speed?
3) Sound travels at around 330m/s. How long does it take to travel one
mile (roughly 1,600m)?
4) Light travels at a speed of 300,000,000m/s. How long would it take to
travel around the world if the diameter at the equator is around
40,000km?
Topic 2 – The Electromagnetic
Specturm
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The Visible Spectrum
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In the 17th Century I did lots of
work on light and wrote about how
visible light was made of the colours
of the spectrum.
Isaac Newton,
1643-1727
Wilhelm
Ritter, 17761810
I accidentally discovered that, if
you put a thermometer here, it
gets hot. I discovered Infra Red
radiation!!
I then discovered
ultra violet by
observing how salts
made from silver
were lightened by
something just
beyond violet light.
William Herschel,
1738-1822
Electromagnetic Radiation
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E-M radiation is basically a movement of energy in the form of
a wave. Some examples:
The Electromagnetic Spectrum
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Each type of radiation shown in the electromagnetic spectrum has a
different wavelength and a different frequency:
High frequency,
_____ wavelength
Gamma
rays
X-rays
Low frequency, _____
(high) wavelength
Ultra violet
Visible
light
Infra red
Microwaves
Radio/TV
γ
Each of these waves travels at the same speed through a _______
(300,000,000m/s), and different wavelengths are absorbed by different
surfaces (e.g. infra red is absorbed very well by ___________ surfaces).
They all travel as _____ waves. The more dangerous waves are at the high
________ end of the spectrum.
Words – black, transverse, long, short, vacuum, frequency
The Electromagnetic Spectrum
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Type of radiation
Uses
Dangers
Gamma rays
Treating cancer,
sterilisation
Cell mutation
X rays
Medical, airport scanners
Cell mutation
Ultra violet
Sun beds, security
Skin cancer
Visible light
Seeing things, photos
None (unless you
look at the sun)
Infra red
Remote controls, heat
transfer, optical fibres
Skin burns
Microwaves
Satellites, phones
Heating of cells
TV/radio
Communications
Very few
Introduction to Radioactivity
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Some substances are classed as “radioactive” – this means that
they are unstable and continuously give out radiation:
Radiation
The nucleus is more stable after emitting some radiation – this
is called “radioactive decay”. Radiation like this can be either
alpha, beta or gamma radiation.
Ionisation
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Radiation is dangerous because it “ionises” atoms – in other
words, it turns them into ions by “knocking off” electrons:
Ionising radiation is emitted by radioactive sources all the
time. Ionisation transfers energy to cells in living tissue,
causing them to mutate, usually causing cancer.
Topic 3 – Waves and the
Universe
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Space: An introduction
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OUR SUN is one of
millions of stars that
orbit the centre of…
THE UNIVERSE, made
up of everything!!
THE MILKY WAY,
which is one of a billion
galaxies that orbit
AND move away from
the centre of…
How our Earth and the Sun
compare to others…
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Distances in space
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The Sun, our closest star, is 1.6x10-5 light years
away from us.
The next closest star, Proxima
Centauri (4.2 light years away)
The centre of our galaxy, the Milky Way, is
around 26,000 light years away.
The Andromeda Galaxy (our closest galaxy)
– approximately 2.5 million light years away
Observing the Universe
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Consider different types of telescope:
Radio telescopes
Space-based telescopes
The original telescopes were used purely for visible light.
These days, telescopes pick up a wide range of waves. Some
examples...
Hubble Space Telescope (HST)
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• 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
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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
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Cosmic Background Explorer (COBE)
• Operated from 1989 to 1993
• Detected small ripples in the
Cosmic Microwave Background
Radiation (CMBR) reaching the
Earth
Life on Other Planets
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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?
Searching for Aliens
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Humans have been searching for me for over 50 years.
Here are some of the methods they use:
SETI – The Search for Extra Terrestrial Intelligence
Since 1960 a group of astronomers have collectively
been sending out EM signals hoping that someone will
send one back!
Space probes
The Voyager 1 probe, still in operation after over
33 years and still sending signals back to Earth.
Soil samples
Soil samples from the moon
and, in recent years, from
Mars have been sampled.
What are the
advantages and
disadvantages of each
of these methods?
How modern telescopes have helped
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Due to technological advances in telescopes our knowledge
of the universe has been expanded. Some examples:
1) In 1610 I used a telescope to determine the
existence of a galaxy around us – the Milky Way –
due to better magnifications in my telescope.
Galileo
2) Some stars don’t emit visible light, so they are
“seen” by taking infra red photos and then applying
“false colour”:
3) The Hubble Space Telescope has been able to
take measurements to more accurately determine
the age of the universe – around 14 billion years.
Making a simple spectrometer
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Slit
Observing the Universe
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Consider different types of telescope:
Ground-based telescopes
Space-based telescopes
What are the advantages and disadvantages of each?
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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”)
Ground-based telescopes
The Life Cycle of a Star
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Stage 1: Nebulae
A nebulae is a collection of dust, gas and rock.
Some examples of nebulae…
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Dark nebula
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Emission nebula