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IB Physics
Mr. Jean
April 16th, 2013
The plan:
• SL Practice Exam questions
• HL Particle Physics
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Electrons
Protons
Neutrons
Quarks
Gluons
Photos
Gravitons
Weak Bosons
Quest Texas:
• Forget about the quest assignment
• This is not happening since the license is
not going to be renewed until the end of
the year.
• Grrrrrrr……
Reminders:
• April 22nd, 2013
– Mock HL & SL physics exam
• May 6th, 2013
– HL & SL physics exam
Standard Model:
• http://www.youtube.com/watch?NR=1&fea
ture=fvwp&v=2xnsMGNicho
Electron:
• An electron is a fundamental particle of nature.
• It can not be seen by any instrument; however
we can predict it’s properties.
• The electro-magnetic force and fields represent
how the electrons interact with other electrons.
– These interactions create the structure of atoms and
molecules possible.
– They give raise to the various combinations and
complexities around us.
What is in a Proton:
• It is composed of
– Two up quarks
• Charge of +2/3
– One down quark
• Charge of -1/3
• Overall charge is positive
– Summation of charge gives you the total amount of
charge in a proton
• 4/3 + (-1/3) = 3/3 = +1
Neutron:
• It is composed of
– Two down quarks
• Charge of -1/3
– One up quark
• Charge of +2/3
– The summation of charge equals zero which
gives neutrons neutral properties.
Strong Nuclear Force:
• The strong nuclear force is the mediator in the atom which keeps the
protons and neutrons together.
• Gluon exchange is the mechanism that keeps the subatomic
particles inside the proton and neutrons ‘glued’ together.
• The result of this exchange to the strong nuclear force is that the
internal properties of the quarks inside the proton or neutron
change. This causes them to repel or attract each other therefore it
contains their motion restricting the size and shape of the proton or
neutron.
Quark Motion:
• Quark motion in an atom is actually traveling
close to the speed of light.
– The quarks motion and exchange is quite simple for
hydrogen; however as you get more and more
complex the exchange becomes more complicated as
well.
Up Quarks
• The particle itself is a fundamental particle and is too
small to be seen by any imaginable instrument of
observation. So we instead represent the properties that
allow the up quark to interact.
• The central small dot represents the weak charge of the
up quark. This charge entirely separate from electric
charge gives rise to the Weak Nuclear Force.
• This force causes up quarks and down quarks to swap
flavours and its typical range is much smaller than the
diameter of a proton.
Quarks and Electric Charge:
• The volume around the quark represents the
electric charge of the up quark, which has a
positive charge of +2/3 units.
• The electric charge is the generator of the
Electromagnetic Force which has infinite range
although the drop off in strength is pretty
dramatic as we move away from the quark.
• This is caused by the ratio of quarks inside each
proton.
Quark SNF & EM
• The Strong Nuclear Force is the force that holds
quarks together in a proton or neutron.
• And a residuum of this force holds the protons
and neutrons together in the nucleus of atoms.
• This force is a hundred times stronger than the
Electromagnetic force, but its range is limited to
about the size of a proton.
The Down Quark:
• The particle itself is a fundamental particle and is too
small to be seen by any imaginable instrument of
observation. So we instead represent the properties that
allow the down quark to interact.
• The central small dot represents the weak charge of the
down quark. This charge entirely separate from electric
charge gives rise to the Weak Nuclear Force.
– This force causes the down quark to change into an up quark,
and its typical range is much smaller than the diameter of a
proton.
Gluons:
• Gluons mediate the Strong
Force.
• They have no mass, no electric
charge and no weak charge.
• So depicting gluons visually is
a real challenge.
• To begin with, there are eight of
them, and each carries a
combination of color charge.
Color Change is CONSERVED:
• Gluons each carry
a combination of
color charge.
• Secondly, there
are no free gluons,
they exist only
virtually when two
quarks interact.
• We know that when gluons cause two quarks to
interact, the quarks swap color, and since color
is conserved, the gluon must have at least two
colors of its own.
•
We know that the strong force mediated by the gluons increases in strength, as the
quarks get farther apart.
•
This means the gluon field is what is called a flux tube and leads to a gluon shaped
like a string.
Photons:
• Photons are the gauge bosons and the force carriers for
Electromagnetism. Whenever charged particles interact,
photons are exchanged.
• They have no mass, no electric charge, no weak charge,
and no color charge the epitome of almost nothing at all.
• Since they are responsible for all electron and proton
interaction, everything we do in our everyday life from
moving a mouse to running in the park relies on the
exchange of photons.
Photons are Energy:
• They are energy, contained in shifting and changing
Electric and Magnetic Fields.
• Like all particles with no rest mass, photons travel at the
speed of light. They cannot come to rest.
• Photons in the range of visible light carry just enough
energy to excite a single molecule in a photoreceptor cell
of your eye.
Gravitons:
• Gravitons are the force carriers for Gravity.
• Its properties have been extrapolated.
– It is a massless, stable, spin = 2 particle that
travels at the speed of light.
– Gravitons may not be constrained to the
dimensions of space and time that we
experience.
Weak Bosons:
• Weak bosons, also called Intermediate Vector
Bosons, are the exchange particles for the Weak
Nuclear Force.
• There are three of them called W+, W-, and Z0.
– They are very massive, each being 80-90 times as
heavy as a proton.
– Because they are so heavy, the uncertainty principle
allows them only an extremely short range when they
act as force carriers.
Weak Bosons:
• The Weak Nuclear Force has a range only about
1/100 the diameter of a proton.
– The W bosons cause quarks to change flavour (color
charge)
– Z0 has an effect interaction called neutral currents.
• Neutral currents describe the flow of the neutrino and of the
electrons
Thursday:
• Neutrinos
• Higgs Bosons
• Standard Model of physics