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Unit 1 – Universal Unit 1 – Universal PhysicsPhysics

(EdExcel)

Topic 1 – Visible Light and Topic 1 – Visible Light and the Solar Systemthe Solar System

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Our understanding of the Our understanding of the universeuniverse

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Ptolemy, AD 90-168

Copernicus, 1473-1543

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.

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”.

Evidence for the Heliocentric Evidence for the Heliocentric ModelModel

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Galileo, 1564-1642

Jupiter and its moons, as seen through a telescope

The orbits of these moons

I helped develop the modern telescope and made measurements with it that proved that the Copernican model of the solar system was correct.

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Observing the UniverseObserving the UniverseWhat are the

advantages and disadvantages

of each of these methods?

A complex digital

camera will be in here

21/04/23An introduction to WavesAn introduction to Waves

A Wave is a “movement of energy” but NOT a transfer of matter

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Wave definitions…Wave definitions…

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)

21/04/23Transverse vs. longitudinal Transverse vs. longitudinal waveswaves

Transverse waves are when the displacement is at right angles to the direction of the wave.

Longitudinal waves are when the displacement is parallel to the direction of the wave…

Dis

pla

cem

en

t

Direction

Direction

Displacement

Examples – light, other EM waves, some seismic waves

Examples – sound, some seismic waves

21/04/23Refraction through a glass Refraction through a glass block:block:

Wave slows down and bends towards the normal due to

entering a more dense medium

Wave speeds up and bends away from the normal due to entering a less dense

medium

Wave slows down but is not bent, due to

entering along the normal

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RefractionRefraction

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

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LensesLenses

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:Another example:

The lens in the eye is used to focus what we see:

21/04/23Converging and diverging Converging and diverging lenseslenses

CONVERGING (Convex)

Thickest at the centre

DIVERGING (Concave)

Thinnest at the centre

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Ray diagrams for lenses 1Ray diagrams for lenses 1

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

The rays of light are refracted OUTWARDS.

A VIRTUAL image is formed – in other words, the image doesn’t actually exist

F

F

A “distant object” Focal

length

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Lenses in TelescopesLenses in Telescopes

Because stars are very far away, the rays of light from them enter a telescope effectively parallel:

Eyepiece lens

Focal pointObjective lens (convex)

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.

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Mirrors in TelescopesMirrors in TelescopesAstronomical telescopes tend to use large concave mirrors as well as a convex lens. This allows them to collect more light:

Objective lens (convex)

Eyepiece lens

Concave mirrorFlat mirror

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The Wave EquationThe 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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1) A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving?

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?

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?

4) Purple light has a wavelength of around 6x10-7m and a frequency of 5x1014Hz. What is the speed of purple light?

Some example wave equation Some example wave equation questionsquestions

0.2m

0.5m

0.6m/s

3x108m/s

21/04/23Distance, Speed Distance, Speed and Time for and Time for

waveswavesSpeed = distance (in metres)

time (in seconds)

D

TS

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 Topic 2 – The Electromagnetic SpecturmElectromagnetic Specturm

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The Visible SpectrumThe Visible Spectrum21/04/23

Isaac Newton,

1643-1727

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.

William Herschel, 1738-

1822

I accidentally discovered that, if you put a thermometer here, it gets hot. I discovered Infra Red radiation!!

Wilhelm Ritter, 1776-

1810

I then discovered ultra violet by observing how salts made from silver were lightened by something just beyond violet light.

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Electromagnetic RadiationElectromagnetic RadiationE-M radiation is basically a movement of energy in the form of a wave. Some examples:

21/04/23The Electromagnetic The Electromagnetic SpectrumSpectrum

Gamma rays

X-rays Ultra violet Visible light

Infra red Microwaves

Radio/TV

Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency:

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

High frequency, _____ wavelength

Low frequency, _____ (high) wavelength

γ

21/04/23The Electromagnetic The Electromagnetic SpectrumSpectrum

Type of radiation Uses Dangers

Gamma rays

X rays

Ultra violet

Visible light

Infra red

Microwaves

TV/radio

Treating cancer, sterilisation

Medical, airport scanners

Sun beds, security

Seeing things, photos

Remote controls, heat transfer, optical fibres

Satellites, phones

Communications

Cell mutation

Cell mutation

Skin cancer

None (unless you look at the sun)

Skin burns

Heating of cells

Very few

21/04/23Introduction to Introduction to RadioactivityRadioactivity

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.

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IonisationIonisationRadiation 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 Topic 3 – Waves and the UniverseUniverse

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21/04/23Space: An introductionSpace: An introductionOUR SUN is one of millions of stars that orbit the centre of…

THE MILKY WAY, which is one of a billion galaxies that orbit AND move away from the centre of…

THE UNIVERSE, made up of everything!!

How our Earth and the Sun How our Earth and the Sun compare to others… compare to others…

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Distances in spaceDistances in space21/04/23

The Sun, our closest star, is 1.6x10-5 light years away from us.

The Andromeda Galaxy (our closest galaxy) – approximately 2.5 million light years away

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.

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Observing the UniverseObserving the UniverseConsider 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...

21/04/23Hubble Space Telescope Hubble Space Telescope (HST)(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

21/04/23Infra Red Astronomical Satellite (IRAS)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

21/04/23Cosmic Background Explorer Cosmic Background Explorer (COBE)(COBE)

• Operated from 1989 to 1993

• Detected small ripples in the Cosmic Microwave Background Radiation (CMBR) reaching the Earth

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Life on Other PlanetsLife on Other PlanetsResearch 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?

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Searching for AliensSearching for AliensHumans 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 How modern telescopes have helpedhelped

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Due to technological advances in telescopes our knowledge of the universe has been expanded. Some examples:

Galileo

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.

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 Making a simple spectrometerspectrometer

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Slit

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Observing the UniverseObserving the UniverseConsider different types of telescope:

Ground-based telescopes

Space-based telescopes

What are the advantages and disadvantages of each?

21/04/23Benefits of observing above the Benefits of observing above the atmosphereatmosphere

• 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

Clearly, ground-based telescopes are a problem because of a number of things:

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The Life Cycle of a StarThe Life Cycle of a Star

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Stage 1: NebulaeStage 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

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Reflection nebula

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Planetary nebula(This nebula is smaller and will only form a planet)

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Gravity will slowly pull these particles together…

As they move inwards their gravitational potential energy is converted into heat and a PROTOSTAR is formed

Stage 2: ProtostarStage 2: Protostar

21/04/23Stage 3: Main SequenceStage 3: Main Sequence

Our sun is an example of a main sequence star – it’s in the middle of a 10 billion year life span

In a main sequence star the forces of attraction pulling the particles inwards are _________ by radiation pressure acting outwards due to the huge __________ inside the star.

Stars are basically ________ reactors that use _______ as a fuel. During its main sequence a star will release energy by converting hydrogen and helium (light elements) into _________ elements.

Words – heavier, balanced, hydrogen, nuclear, temperatures

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Eventually the hydrogen and helium will run out. When this happens the star will become colder and redder and start to swell…

If the star is relatively small (like our sun) the star will become a RED GIANT

If the star is big (at least 4 times the size of our sun) it will become a RED SUPERGIANT

Stage 4: Red GiantStage 4: Red Giant

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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:

Stage 5: The DeathStage 5: The Death

White dwarf

Black dwarf

Red giant

21/04/232) If the star was a RED SUPERGIANT it will shrink and then EXPLODE, releasing massive amounts of energy, dust and gas.

AfterBefore

This explosion is called a SUPERNOVA

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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.

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The dust and gas thrown out by a supernova can be used to form a new star…

Stage 6: Second generation starsStage 6: Second generation stars

Our sun is believed to be a “______ ______ star” – this is because it contains some __________ elements along with hydrogen and ________. These heavier elements would have been the products of a previous star that have been thrown out by a ________. These heavier elements are also found on planets, indicating that they might have been made from remains of previous _______ as well.

Words – helium, heavier, second generation, stars, supernova

21/04/23The formation of the The formation of the universeuniverse

The “Steady State” theory

This theory states that the universe has always existed as it does now and hasn’t changed. The trouble is that the night sky would be completely lit up because of the billions of stars, but it’s not, so…

The “Big Bang” theory

This theory states that the universe started off with an explosion and everything has been moving away ever since. There are two main pieces of evidence for this: background microwave radiation and red shift.

There are two main theories about how the universe started:

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Evidence about the Evidence about the origins of the universe…origins of the universe…

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MicrowavesMicrowavesWhen the “Big Bang” happened microwaves were produced and these are still reaching us now. They can sometimes be seen as TV interference.

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Source of light “Spectra

”

Red Shift explainedRed Shift explained

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If you pass the light through a gas something different is seen…

helium

Some wavelengths of light are absorbed by

the gas – an “absorption spectrum”.

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After

helium

If the light source is moving away the absorption spectra look a little different…

helium

Before

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After

Before

A similar effect happens with sound – this is called “The

Doppler Effect”Hear Doppler Effect

This is called red shift. The faster the light source moves the further its light will be “shifted”

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Red Shift simplifiedRed Shift simplified

Basically, if I walk towards you I’ll look slightly more blue. Then, if I

walk away from you, I’ll look slightly more red!!

Let’s try it…

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Light from different stars and from the edge of the universe also shows this “red-shift”. This suggests that everything in the universe is moving away from a single point.

This is the BIG BANG theory

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Red shift summaryRed shift summaryLight from other galaxies has a longer _________ than expected. This shows that these galaxies are moving ____ from us very quickly. This effect is seen to a greater extent in galaxies that are _______ away from us. This indicates that the further away the galaxy is, the ______ it is moving.

Words to use – faster, away, universe, big bang, billion, wavelength, further

This evidence seems to suggest that everything in the universe is moving away from a single point, and that this process started around 14 _____ years ago. This is the ____ ________ Theory. Further evidence of this theory is Cosmic Microwave Background Radiation (CMBR) – this radiation comes from the Big Bang and fills the _________.

Big Bang Theory vs Steady Big Bang Theory vs Steady StateState

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Some scientists have explained that red shift can actually be used to support the Big Bang Theory – this explanation is based around the rates of expansion and contraction of different galaxies. If our neighbouring galaxy is expanding at a different rate to the Milky Way then it will appear red or blue-shifted.

Stephen Hawking, 1942 -

However, the discovery of CMBR was the final nail in the coffin for the Steady State theory. So, Mr President, the Big Bang theory is now the widely accepted theory of how the universe began.