MEDI 11002 Lecture Notes - Lecture 6: Electric Field, Fundamental Interaction, Corona
Alicia Gracie
1 | P a g e
CHAPTER 6 – MATTER, RELATIVITY AND ASTRONOMY
EXTENDING OUR MODEL OF MATTER:
Physicists get a new toy
- LHC (Large Hadron Collider)
o Switched on in 2008
o Found 100m underground
o Accelerates protons and lead ions in opposite directions
o Resulting fragments are studied in order to discover new particles and creates
the quark-gluon plasma (thought to have existing after the big bang)
- This collider is hoped to help extend the standard model of matter
As far as you need to know…
- As far as scientists know; protons, neutrons and electrons are the fundamental
particles in nature
- In the latter stages of WW2, physicists noticed that new particles were being
formed by bombarding energy of particles
- They needed to build more powerful machines to accelerate protons and electrons
to energies high enough to form particles that they were predicting that existed
Resolving small particles
- The ability to resolve small particles is related to the wavelengths of the light that
is used to illuminate the particles
- Diffraction occurs when wavelengths
have a greater width than the width of
the particle itself
- Scattering occurs when the wavelength
is the same size or smaller than the
object
- Electromagnetic waves → matter =
smaller wavelengths to probe nucleus
Force fields or particle exchange
- Electric field will cause a positively charged particle to move under the influence
of an electromagnetic force
o Electric field is a component of electromagnetic radiation
o This propagates as a wave and is able to spread the electric force
- Light also travels as a particle called a photon
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Alicia Gracie
2 | P a g e
- The force between two particles results
from an exchange of a force-carrying
particle between the two, causing a
repulsive force on each charged particle
Feynman diagrams
- Diagrams based on quantum
electrodynamics
o Explain the interaction between two
charged particles
o Arrows indicate the type of particle
- The Feyman diagram shows the photon being exchanged between the two
electrons
o This photon cannot be detected and is therefore referred to as a virtual
photon
o As the photon mediates the electromagnetic force, then there must be a
particle that mediates the strong nuclear force
- Gluons are named so because they glue the nucleus together
The four forces in nature and their mediating particles
There are four known fundamental forces of nature:
1. Strong nuclear force – gluon
2. Electromagnetic force – photon
3. Weak nuclear force – W+, W- and the Z0 particles
4. Gravity – unknown particle; being researched (graviton)
Matter and antimatter
- Each matter particle has an opposite antimatter particle
o E.g. Electron → ANTIMATTER PARTICLE → Positron
o There is also the anti-proton and anti-neutron
- Antimatter is greatly outnumbered in the universe by normal matter
- When normal matter and its antimatter equivalent collide, they convert their
masses into energy
o This is called annihilation
Classifying these new particles:
- BOSONS
o Strong nuclear
o Electromagnetic and
o Weak forces
o Includes:
Gluons
Photons and
W and Z particles
- LEPTONS
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Alicia Gracie
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o Interact by exchanging W and Z bosons (mediate weak nuclear force)
o Leptons that carry a charge can also interact by exchanging photons – they do
not interact via strong force carriers
o These include:
Electron
Muon and
Tau particles
Neutrinos and antimatter opposites of these
- HADRONS
o Baryons and mesons
o All interact by exchanging gluons
o If they carry a charge they may interact by exchanging photons
- MESONS
o Assigned a baryon number of 0
o Many different articles and their anti-particles
o These include:
Pion and anti-pion
Kaon and antikaon
And the eta ( has no antimatter because it is considered to be so itself)
- BARYONS
o Assigned a baryon number of 1 for normal matter and -1 for antimatter
o Includes:
Proton and antiproton
Neutron and antineutron
Lambda-zero and antilambda-zero atc
As far as they know
- WHAT FLAVOUR QUARK WOULD YOU LIKE?
o Up
o Down
o Strange
o Charmed
o Bottom
o Top
o Properties of a baryon number
o Colour change which is similar to an electric charge
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