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Particles and Quantum Phenomena

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The pair consists of one particle and its antiparticle. ... Wave Particle Duality. So you though everything is a wave or a particle yeh? ... – PowerPoint PPT presentation

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Title: Particles and Quantum Phenomena


1
Particles and Quantum Phenomena
2
What Are the 4 Fundamental Forces?
3
Fundamental Forces
  • Electromagnetic
  • Gravitational
  • Nuclear weak
  • Nuclear strong

4
Gravity
  • What are/is the exchange bosons?
  • What do they act between?
  • Is it weak or strong?

5
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!)

6
Electromagnetic
  • What are/is the exchange bosons?
  • What do they act between?
  • Is it weak or strong?

7
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

8
Nuclear Weak
  • What are/is the exchange bosons?
  • What do they act between?
  • Is it weak or strong?

9
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!)

10
Nuclear strong
  • What are/is the exchange bosons?
  • What do they act between?
  • Is it weak or strong?

11
Nuclear strong
  • What are/is the exchange bosons?
  • Gluons
  • What do they act between?
  • Quarks
  • Is it weak or strong?
  • Very strong

12
Particles and Anti Particles
  • All particles have an antiparticle
  • Anti particles have the same
  • But opposite

13
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?

14
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?

15
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)

16
Observing particles
  • How do we see particle collisions annihilations
    etc?

17
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?

18
Particle tracks
  • What could this be?

19
Particle tracks
  • Pair creation
  • Why do they curve different ways?

20
Particle Families
  • What are the main ones?

21
Particle families
  • The main groups are -
  • Hadrons
  • Leptons

22
Leptons
  • What type of particle are they?
  • What is the simplest?

23
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?

24
Basic lepton family
  • Electron e- and
  • Positron e
  • Electron neutrino ?e and
  • Anti electron neutrino ?e
  • What about the excited lepton family?

25
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!

26
Hadrons
  • What is the basic property?

27
Hadrons
  • These are heavy (e.g. contain a relatively big
    mass)
  • They are made from Quarks
  • But what are the two sub sets?

28
Hadrons
  • They are split into two sub sets-
  • 1 Baryons
  • 2 Mesons
  • What is the difference?

29
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?

30
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?

31
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

32
Quarks
  • What are they?
  • What types are there?
  • What properties do they have?

33
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!

34
Conservation Laws
  • Lepton number is .. conserved.
  • Baryon number is .. conserved.
  • Charge is conserved.
  • Strangeness . But..

35
Conservation Laws
  • Lepton number is ALWAYS conserved.
  • Baryon number is ALWAYS conserved.
  • Charge is ALWAYS conserved.
  • Strangeness CAN change but only in weak decays.

36
Feynman Diagrams
  • Sorry you have just got to learn them!
  • But what dont they show us?

37
Feynman Diagrams
  • They DONT show DIRECTION
  • Have you learnt them?

38
Refraction
  • When light passes from one material to the other,
    which of the following changes?
  • Wavelength
  • Speed
  • Direction
  • Frequency
  • Colour

39
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

40
What about Air to Glass
  • Do the following increase or decrease?
  • Wavelength
  • Speed
  • Direction
  • Frequency

41
Air to glass(optically less dense to dense)
  • Wavelength Shortens
  • Speed Slows
  • Direction Refracted TOWARDS the Normal
  • Frequency Stays the same

42
Glass to Air(Optically More Dense to Less Dense)
  • Wavelength increases
  • Speed increases
  • Direction refracted AWAY from the normal
  • Frequency stays the same

43
Snells Law
  • This shows us the relation ship between the
    speeds and the sine of the angles of incidence
    and refraction.
  • What is it?

44
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

45
Refractive index going from two different
materials
  • Eg from glass to water
  • How could you work it out?

46
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?

47
  • 1n2 n2 / n1
  • Eg Water n 1.33 Glass n 1.54
  • So refractive index from water to glass -
  • wng 1.54/1.33

48
The critical angle?
  • What is it all about and why is it so critical?

49
The critical angle
  • This is the maximum angle of incidence that light
    can be refracted and pass through a boundary!
  • Eh?

50
Remember the diagram!
The critical angle
51
How about the equation?
52
  • Sin ?c 1/n

53
  • 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!

54
You need to explain about -
  • Optical fibres
  • The cladding ( lower refractive index surrounding
    the higher refractive index core)
  • Modern applications in-
  • Endoscopy
  • communications

55
The Photoelectric Effect
  • What is incident on the metal surface?
  • What comes out from the surface?

56
The Photoelectric Effect
  • What is incident on the metal surface?
  • Photons
  • What comes out from the surface?
  • Photoelectrons

57
What about energy?
  • What gives up its energy?
  • Where does it go?

58
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?

59
Einstein's Photoelectric Equation
  • Energy of Photon (E hf)
  • hf F Ek
  • Work function
  • Maximum Kinetic energy

60
What is the work function etc?
61
  • F the work function or the energy required to
    remove an electron from the metals surface.

62
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?

63
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!

64
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?

65
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)

66
What if the frequency is really low?
  • As the frequency gets lower the maximum kinetic
    energy of each photoelectron gets lower until.

67
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.

68
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

69
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

70
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.

71
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.

72
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.

73
What Is the Equation That Enables Us to Work Out
the Frequency Given Out?
74
  • hf E1 E2
  • hf energy of photon given out
  • E1 Energy of electron level 1
  • E2 Energy of electron level 2

75
Uses of excitation
  • You need to know about ionisation and excitation
    in the fluorescent tube.
  • Look it up if you dont!!

76
Thought Id Save the Impossible to Last!
  • Read on unless you are schizophrenic!!
  • Sorry did someone say something?

77
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!

78
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!)

79
What is the equation?
  • ? h/mv
  • ? Wavelength associated with particle of
    momentum mv
  • h Plancks constant.

80
You Need to Remember That Electron Diffraction
Through Layers of Graphite Atoms Give Us Evidence
of the Wavelike Behaviour of Electrons.
81
Thats All Folks!
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