IB Physics

Mr. Jean

April 16th, 2013

The plan:

• SL Practice Exam questions• HL Particle Physics

– 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&feature=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