Particles and Quantum Phenomena

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Particles and Quantum Phenomena
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What Are the 4 Fundamental Forces?
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Fundamental Forces

• Electromagnetic
• Gravitational
• Nuclear weak
• Nuclear strong

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Gravity

• What are/is the exchange bosons?
• What do they act between?
• Is it weak or strong?

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Gravity

• What are/is the exchange bosons?
• Gravitons
• What do they act between?
• All particles with mass
• Is it weak or strong?
• Very weak (it only feels big because the Earth is
  so big!)

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Electromagnetic

• What are/is the exchange bosons?
• What do they act between?
• Is it weak or strong?

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Electromagnetic

• What are/is the exchange bosons?
• Photons
• What do they act between?
• Charged particles
• Is it weak or strong?
• Very strong compared to gravity

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Nuclear Weak

• What are/is the exchange bosons?
• What do they act between?
• Is it weak or strong?

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Nuclear weak

• What are/is the exchange bosons?
• W, W-, Z
• What do they act between?
• Nucleons
• Is it weak or strong?
• Weak (compared to nuclear strong!)

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Nuclear strong

• What are/is the exchange bosons?
• What do they act between?
• Is it weak or strong?

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Nuclear strong

• What are/is the exchange bosons?
• Gluons
• What do they act between?
• Quarks
• Is it weak or strong?
• Very strong

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Particles and Anti Particles

• All particles have an antiparticle
• Anti particles have the same
• But opposite

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Particles and Anti Particles

• All particles have an antiparticle
• Anti particles have the same mass
• But opposite charge
• What happens if they come across each other?

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Annihilation

• This happens when a particle and its antiparticle
  meet.
• The result is 2 or 3 Gamma rays are given out
  and the particles disappear.
• What is the opposite of Annihilation?

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Pair production

• If a gamma Ray interacts with something e.g. an
  atom/electron and it has enough energy a pair of
  particles may be produced.
• The pair consists of one particle and its
  antiparticle.
• (The atom/electron has to be there so that
  momentum is conserved)

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Observing particles

• How do we see particle collisions annihilations
  etc?

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Cloud chambers and Bubble chambers

• Both of these enable us to see the paths of
  particles by observing the ionisation caused by
  the tracks.
• If a magnetic field is present the tracks are?

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Particle tracks

• What could this be?

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Particle tracks

• Pair creation
• Why do they curve different ways?

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Particle Families

• What are the main ones?

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Particle families

• The main groups are -
• Hadrons
• Leptons

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Leptons

• What type of particle are they?
• What is the simplest?

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Leptons

• They are light (relatively small mass) particles
• The simplest is the electron
• What are the other three particles that make up
  the basic family?

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Basic lepton family

• Electron e- and
• Positron e
• Electron neutrino ?e and
• Anti electron neutrino ?e
• What about the excited lepton family?

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Excited Lepton Family

• Muon µ
• Anti Muon
• Muon neutrino ?µ and
• Anti Muon neutrino
• The Tau family is the last in the series but
  should not be needed!

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Hadrons

• What is the basic property?

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Hadrons

• These are heavy (e.g. contain a relatively big
  mass)
• They are made from Quarks
• But what are the two sub sets?

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Hadrons

• They are split into two sub sets-
• 1 Baryons
• 2 Mesons
• What is the difference?

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Baryons and Mesons

• Baryons are made up of three Quarks
• Mesons are made up of two Quarks (one normal and
  one anti quark)
• What are the common Baryons?

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Baryons

• Neutrons, protons, sigma's S, omegas O
• And their anti particles
• All of these have a baryon number of
• 1 or 1
• What about the mesons? What are the common ones?

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Mesons

• These are made of two quarks one quark and one
  anti quark
• There are p mesons (often called pions)
• And ? mesons (often called Kaons)
• They may have charge of 1, -1 or 0

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Quarks

• What are they?
• What types are there?
• What properties do they have?

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Quarks

• What are they? Fundamental particles!
• What types are there?
• Up, down, strange, charm, top and bottom. (These
  are sometimes called flavours of quark!) There
  are also anti-quarks which have opposite charge.
• What properties do they have?
• Mass, charge, baryon numbers of 1/3 or 2/3 and
  lepton numbers of 0!

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Conservation Laws

• Lepton number is .. conserved.
• Baryon number is .. conserved.
• Charge is conserved.
• Strangeness . But..

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Conservation Laws

• Lepton number is ALWAYS conserved.
• Baryon number is ALWAYS conserved.
• Charge is ALWAYS conserved.
• Strangeness CAN change but only in weak decays.

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Feynman Diagrams

• Sorry you have just got to learn them!
• But what dont they show us?

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Feynman Diagrams

• They DONT show DIRECTION
• Have you learnt them?

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Refraction

• When light passes from one material to the other,
  which of the following changes?
• Wavelength
• Speed
• Direction
• Frequency
• Colour

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Refraction

• When light passes from one material to the other
  the following things happen-
• Wavelength Changes
• Speed Changes
• Direction Changes (if not at 00 !)
• Frequency Stays the same
• Colour Stays the same

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What about Air to Glass

• Do the following increase or decrease?
• Wavelength
• Speed
• Direction
• Frequency

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Air to glass(optically less dense to dense)

• Wavelength Shortens
• Speed Slows
• Direction Refracted TOWARDS the Normal
• Frequency Stays the same

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Glass to Air(Optically More Dense to Less Dense)

• Wavelength increases
• Speed increases
• Direction refracted AWAY from the normal
• Frequency stays the same

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Snells Law

• This shows us the relation ship between the
  speeds and the sine of the angles of incidence
  and refraction.
• What is it?

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Snells Law

• 1n2 sin i c1 speed in material 1
• sin r c2 speed in material 2
• Refractive index going from material 1 to 2

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Refractive index going from two different
materials

• Eg from glass to water
• How could you work it out?

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Refractive index going from two different
materials

• Eg from glass to water
• Yes you divide one refractive index by the other
  but which way round??
• What is the formula?

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• 1n2 n2 / n1
• Eg Water n 1.33 Glass n 1.54
• So refractive index from water to glass -
• wng 1.54/1.33

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The critical angle?

• What is it all about and why is it so critical?

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The critical angle

• This is the maximum angle of incidence that light
  can be refracted and pass through a boundary!
• Eh?

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Remember the diagram!
The critical angle
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How about the equation?
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• Sin ?c 1/n

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• Dont forget Total internal reflection only
  happens trying to go from more dense to less
  dense.
• Also if you do 1/n and inverse sine on your
  calculator and you get an error you have got the
  wrong n!!!
• Just invert the number youve got!

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You need to explain about -

• Optical fibres
• The cladding ( lower refractive index surrounding
  the higher refractive index core)
• Modern applications in-
• Endoscopy
• communications

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The Photoelectric Effect

• What is incident on the metal surface?
• What comes out from the surface?

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The Photoelectric Effect

• What is incident on the metal surface?
• Photons
• What comes out from the surface?
• Photoelectrons

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What about energy?

• What gives up its energy?
• Where does it go?

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What about energy?

• What gives up its energy?
• The Photon
• Where does it go?
• To remove the photoelectron and give it Kinetic
  energy
• What is the Nobel prize winning equation?

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Einstein's Photoelectric Equation

• Energy of Photon (E hf)
• hf F Ek
• Work function
• Maximum Kinetic energy

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What is the work function etc?
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• F the work function or the energy required to
  remove an electron from the metals surface.

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What happens if you change the conditions?

• Eg if the intensity of light is increased?
• What happens to the number of photons?
• What happens to the maximum kinetic energy?

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What happens if you change the conditions?

• Eg if the intensity of light is increased?
• What happens to the number of photons?
• It increases!
• What happens to the maximum kinetic energy?
• It stays the same! The frequency stays the same!

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What happens if you change the conditions?

• Eg if the frequency of the light is decreased?
• What happens to the number of photons?
• What happens to the maximum kinetic energy?

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What happens if you change the conditions?

• Eg if the frequency of the light is decreased?
• What happens to the number of photons?
• It stays the same! (The intensity is the same)
• What happens to the maximum kinetic energy?
• It decreases. (there is less energy contained in
  EACH photon so less available for EACH
  photoelectron)

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What if the frequency is really low?

• As the frequency gets lower the maximum kinetic
  energy of each photoelectron gets lower until.

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What if the frequency is really low?

• As the frequency gets lower the maximum kinetic
  energy of each photoelectron gets lower until.
• There is no longer enough energy available to
  overcome the work function. The result is no
  photoelectrons are ejected.
• The lowest frequency possible is called the
  threshold frequency.

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The electronvolt

• First a quick reminder of the definition of a
  volt-
• 1 Joule is the work done moving one coulomb of
  charge through one volt.
• Or Energy Charge x Voltage

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So what about the electronvolt?

• This is the energy required to accelerate one
  electron through one volt!
• But E Q x V
• So 1eV 1.6 x 10 19 J Or
• 1J 1/1.6 x 10 19 eVs

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Energy Levels in Atoms

• All .. in atoms are held in fixed precise
  energy levels.
• Each electron is in a .. energy level.
• Electrons cannot occupy the same as another
  electron.
• When electrons Jump between levels an ..
  amount of energy is given out or taken in.

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Energy Levels in Atoms

• All electrons in atoms are held in fixed precise
  energy levels.
• Each electron is in a different energy level.
• Electrons cannot occupy the same level as another
  electron.
• When electrons Jump between levels an exact
  amount of energy is given out or taken in.

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Evidence That Suggests This

• Line spectra (Eg Sodium lamp)
• The light given out is of an exact wavelength and
  frequency.
• This corresponds to an exact change in energy of
  an excited electron from a high level to a lower
  level.

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What Is the Equation That Enables Us to Work Out
the Frequency Given Out?
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• hf E1 E2
• hf energy of photon given out
• E1 Energy of electron level 1
• E2 Energy of electron level 2

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Uses of excitation

• You need to know about ionisation and excitation
  in the fluorescent tube.
• Look it up if you dont!!

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Thought Id Save the Impossible to Last!

• Read on unless you are schizophrenic!!
• Sorry did someone say something?

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Wave Particle Duality

• So you though everything is a wave or a particle
  yeh?
• Well life is not that easy in fact its totally
  impossible to understand!!
• Dont give in though the equation is easy even if
  the end result is quantum mechanics that NOBODY
  understands!

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de Broglie and his wavelength

• de Broglie postulated that every particle
  exhibits wavelike behaviour but that all waves
  also exhibit particle like behaviour.
• (waves are particles and particles are waves!)

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What is the equation?

• ? h/mv
• ? Wavelength associated with particle of
  momentum mv
• h Plancks constant.

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You Need to Remember That Electron Diffraction
Through Layers of Graphite Atoms Give Us Evidence
of the Wavelike Behaviour of Electrons.
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Thats All Folks!