Chapter 17 - Probing Deep into Matter

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Resources: Page numbers refer to your Advancing Physics textbook, codes to the CD. Access to Advanced Level Physics and Physics Foundation Unit are available from your teacher.

Key: Demo = Demonstration, Pres = Presentation, SoftAct = Software Activity, Exp = Experiment, Home = Home Experiment, Dis = Display

SAQ = Short Answer Question, Est = Estimate, Comp = Comprehension, Data = Data Handling, ExExQ = Explanation-Exposition Question, Warm = Warm Up Exercise Question, MC = Multiple Choice Question

Work in class

Work out of class

17.1 Creation and annhilation
Lesson 1 Bubble chambers and pair production

Objectives: - all the words for particles and interactions: matter, antimatter, electron, proton,
neutron, lepton, baryon, neutrino, meson
- all the conservation laws - momentum, energy, charge

Activity Reading 20T 'Three poems about particles'
Reading 30T 'Early ideas about elementary particles'

What happened with beta decay and the neutrino.
Reading 10T 'The discovery of beta decay'
SoftAct 10S 'Bubble chamber photographs' as a demo
Cloud chambers - how to 'see' particles
http://www.ap.smu.ca/demos/content/modern/alpha_particles_in_a_cloud
_chamber/ alpha_particles_in_a_cloud_chamber.html

Pair production -what does it mean? Particles and their classification:
lepton (light) number/particles = electrons, neutrinos (or anything equal to or lighter than the electron)
baryon (heavy) number/particles = everything else (protons, neutrons, everything made of quarks that is heavier (or equal to) the proton))
Dis 20O 'Making PET scans'
Dis 30O 'Conserved quantities in electron-positron annihilation'
Dis 40O 'Pair creation and annihilation'
Dis 50O 'Quantum fields create and destroy particles'

SAQ 10S 'Things that don't change'

Lesson 2/3 Interactions and particles
Objectives: - there are matter particles and force particles, fermions and bosons
- which forces are mediated by which particles]
- Feynmann diagrams are a neat way of showing interactions

SAQ 30S 'Creation and annihilation'

A new way to look at fields: The forces between things are due to exchange of particles:
SoftAct 30S 'Interactions in particle physics'
Book page 177/178 and discuss Feynmann diagrams
There is a difference
http://www2.slac.stanford.edu/vvc/theory/feynman.html
Dis 90O 'Identical particles - bosons and fermions
Thats why you don't fall through the floor.
Fermions (electron, proton, neutron, neutrino..) are matter particles (spin = 1/2)
Bosons (photons, gluons, W and Z particles and gravitons(?)) are field particles (spin = 0)

Relativity and particle physics - who ordered that?
SoftAct 40S 'Time and the Muon'
SoftAct 50S 'Identifying particles using Lancaster Particle Physics software'
and.. Why did the chicken cross the road?
http://www.xs4all.nl/~jcdverha/scijokes/2.html#chicken_11

Comp 50C 'Creation from annihilation'
MC 40M 'Particles and interactions'
MC 60M 'Keeping momentum and energy unchanged'

Extension: a) Reading 50T Text to Read 'Where did all the antimatter in the Universe go?'
b) Reading 60T Text to Read 'Symmetry and conservation laws'

Quick check - do you know:
particles can be created and annihilated in matter-antimatter pairs.
electrons and positrons have opposite charges and lepton numbers.
electromagnetic interactions arise from the exchange of photons.
electrons are fermions, which obey the Pauli exclusion principle.
leptons are particles like the electron, neutrino and their antiparticles.
total energy, momentum and charge are conserved in interactions.

 

 

 

17.2.1 How big are nuclei?
Lesson 4 How big are nuclei?

Objectives - scattering experiments involve firing particles at matter
- what they do tells us what matter is made of
- Rutherford did it with alpha particles to find out about the atom

The history of ideas about the atom and how scientists have found out.
http://www.emsb.qc.ca/laurenhill/science/models.html

How do you find out?
Exp 70E 'Probing arrangements'
Dis 110O OHT 'Alpha particle scattering experiment'
SoftAct 80S 'Probes scattered by a target'
SoftAct 90S 'Many probes scattered by a target'
SoftAct 100S 'Where scattered probes go'
Dis 120O OHT 'Rutherford's picture of alpha particle scattering'

Run Rutherford Scattering applet from:
http://phet.colorado.edu/new/get_phet/simlauncher.php
Summary notes on distance of distance of closest approach and sketches of the shape of the path of a scattered alpha particle. A charged particle needs energy of several MeV to get close to a nucleus.


Lesson 5 Calculating distances etc.
Objectives: - you can work out how far a particle can get to a nucleus

Look in book page 184 or Display Material 130O OHT 'Distance of closest approach'
SAQ 80S 'Rutherford scattering: directions of forces'
SAQ 70S 'Rutherford scattering: energy and closest approach'

Lesson 6 Inside the nucleus
Objectives: - nuclei are very dense
- the volume of a nucleus is proportional to the number of nucleons
- you need big energies to go deep into matter
- nuclei are made of quarks there are rules for putting them together to make hadrons and mesons

How dense is dense?
Work out the density of the nucleus of Helium. Work out the mass of a dice sized piece of it.

SoftAct 130S 'The density of nuclear matter'
+ look at page 187 or Dis 140OOHT 'Density of nuclear matter'
The volume of a nucleus is proportional to the number of nucleons - link to the mass of neutron stars.
Probing smaller and smaller things requires larger and larger accelerators and higher energies. Geiger and Marsden's apparatus fitted on a table top; a detector at CERN is a big as a small house
Dis 150O OHT 'Deep inelastic scattering'
Look at page 188 in the book or Dis160 OOHT 'Quarks and gluons'
Pres 60P 'Quark models'
SAQ 110S 'Putting quarks together'
SAQ 90S: Electrons measure the size of nuclei

 

1.Questions page 181
2. SoftAct 110S 'The Livingston curve'
3. SoftAct 120P Presentation 'The funding of particle physics'
4. Reading 80T Text to Read 'Tracking particles'

Extension: a) SAQ 100S Scattering and scale
b) Reading 70T Text to Read 'Towards a nuclear atom'
c) Comp 120C 'Finding parts of protons'
d) Reading 80T: Text to Read 'Tracking particles'

Quick check - do you know:

scattering experiments reveal the structures of atoms, nuclei and nucleons; the smaller the
scale the greater the energy needed
atoms have tiny dense positively charged nuclei, made of protons and neutrons packed
together at high density
quarks with fractional electric charges combine in threes to form neutrons, protons and
other particles
the strong 'colour' force between quarks is carried by gluons, which like photons are
bosons. Particles which 'feel' this force are called hadrons.
at high energies, scattering experiments create a large number of new kinds of particle

17.3 The music of the atoms

Lesson 7 Standing waves in atoms
Objectives - standing waves have certain wavelengths
- we can think of electron waves as fitting into an atom as a standing wave
- if so they can only have certain wavelength, frequencies and energies.

Standing waves on a string again.

Electron diffraction expt again. How do you resolve fact that electrons are wavy with them having orbits?

Looking back at standing waves
Exp 140E 'Standing waves - for electrons?'
+ look at page 193
Electrons in atoms have particular wavelengths, so have particular energies.
Work out k.e. and p.e. (see page 94).
SoftAct 150S 'Sizing up a hydrogen atom'

Lesson 8 Energy levels and transitions
Objectives - only certain energies are allowed
- electrons make transitions between them by absorbing or emitting photons.

If you look at gas tubes through diffraction glasses you see line spectra.
The upshot being that only discrete energy levels are allowed - see page 94
SAQ 150S 'Spectra and energy levels'
Dis 200O OHT 'Standing waves in atoms'
Dis 210O OHT 'Size of the hydrogen atom'
SAQ 170S 'Carrots and guitar strings'
Dis 220O OHT 'What the world is made of'

17.3.3 Some more questions
SAQ 170S 'Carrots and guitar strings'
Data 180D 'Products of the Big Bang'
Comp 140C 'How Niels Bohr began quantum theory'
Dis 220O OHT 'What the world is made of'

SAQ 160S 'How small could a hydrogen atom be?'
Data 180D 'Products of the Big Bang'
Comp 140C 'How Niels Bohr began quantum theory'
Extension: a) Reading 40T: Text to Read 'Quantum theory in the twentieth century'


Quick check - do you know:
electrons confined in a region of space can be modelled as standing waves, with wavelengths determined by the size and shape of the confining region
the de Broglie wavelength is

discrete atomic energy levels correspond to discrete electron standing waves in an atom.
eletrons can make quantum jumps between allowed energy levels, emitting or absorbing a photon whose energy is given by

the energy level spacings in hydrogen are given by

where n is the principal quantum number.



 

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