5.3 Probing Deep Into Matter Flashcards
What did Rutherford’s experiment involve?
Firing a stream of alpha particles at a thin gold foil and recording the number of alpha particles scattered at different angles.
Alpha particles can be scattered at angles greater than 90º this can only happen if…
The object they’re striking is more massive than themselves.
Give evidence that supports the idea that the atom is mostly empty space.
Most fast, charged alpha particles go straight through gold foil.
Some alpha particles are reflected back form the gold foil through significant angles. What does this mean?
The centre of the atom must be tiny but have a lot of mass.
All alpha particles fired at a gold foil were repelled, what does this mean?
The nuclease has a positive charge.
Explain why electrons must be on the outside of the atom.
Atoms are neutral overall but have appositively charged nuclease at their centres.
What are atoms made up of?
Protons, neutrons and electrons.
Describe what happens as an alpha particle is deflected by a nucleus.
The kinetic energy of the alpha particle is converted into electric potential energy as it approaches the nucleus. This is then converted back into kinetic energy as it is deflected.
Give the equation you can use to find the closest approach of an alpha particle to the nucleus.
Initial KE = kQq/r
What are hadrons?
Particles that feel the strong interaction.
What holds protons and neutrons together in the nucleus of an atom.
The strong force.
What are the fundamental particles that make up hadrons?
Quarks.
What are the two types of hadrons?
Baryons and mesons.
Give two nucleons.
Protons and neutrons.
Which particle is the only stable baryon?
The proton.
How many quarks make up a baryon?
Three.
What is the composition of a meson?
A quark and an antiquark.
What is the baryon number and what happens to it in a reaction?
The number of baryons in a system. It is always conserved.
What are leptons?
Fermions that don’t feel the strong interaction.
Are leptons fundamental particles?
Is the sky blue?
Give three ways that leptons can interact.
Weak interaction, gravity and electromagnetic.
Name three leptons.
Electrons, e-, muons, μ- and tau, τ-.
What happens to muons and taus?
They are unstable so decay into electrons.
What are neutrinos?
Particles that have (almost) zero mass and zero charge. Electrons, muons, and taus have their own neutrino.
What is the symbol for neutrino?
𝑣
How many types of lepton number are there?
Three.
What happens in a β- decay?
Neutrons decay into protons.
Give the equation for a β- decay.
n → p + e- + ṽe
What is a positron?
The electron’s antiparticle. It has the same mass but opposite charge.
What is the lepton number of a position?
-1
Every particle has an…
Antiparticle
Give the equation for the equivalence of energy and mass.
E = mc^2
When energy is converted into mass…
equal amounts of matter and antimatter are made.
What happens if you fire two very high energy protons at each other?
An extra proton and therefore an antiproton is created. This is pair production.
What produces an particle-antiparticle pair?
A high energy gamma photon.
What is the most common pair of particles to be produced from pair production?
Electron-position pairs since they have a relatively low mass.
What is the opposite of pair production?
Annihilation.
When does annihilation occur?
When a particle meets its antiparticle.
What happens during annihilation?
The particle-antiparticle pair get converted into energy in the form of two gamma photons.
Why are you unlikely to detect antiparticles?
Because they only exist for small fractions of a second before they are annihilated.
What are quarks?
Fundamental particles that are the building blocks of hadrons.
Name six quarks.
Up, down, strange, charm, top and bottom.
What are antiparticles of hadrons made from?
Antiquarks.
What is the baryon number of an antiquark?
-1/3
Which combination of quarks make up a proton?
uud
Which combination of quarks make up a neutron?
udd
Can quarks exist on their own?
Certainly not.
What happens when you use energy to attempt to isolate a quark.
The energy is converted to a quark-antiquark pair.
What are gauge bosons?
Exchange particles - virtual particles that allow the interaction of other particles.
What is the gauge boson of the strong force?
The gluon.
What is the exchange particle of the electromagnetic force?
The photon.
Name the gauge bosons for the weak force.
W-, W+ and Zº
What happens to the gluon field between two quarks as you try to separate them?
The energy in the field increases, increasing the attraction between them until the field has enough energy for pair production.
What does a linear particle accelerator consist of?
A long straight tube containing a series of electrodes.
How do linear particle accelerators work?
Timed AC is applied to the electrodes so that the particles are always attracted to the next electrode and repelled form the previous one.
What leaves a linear particle accelerator?
High energy particles travelling close to the speed of light.
What does a cyclotron consist of?
Two semicircular electrodes.
How do cyclotrons work?
Alternating p.d. is applied between the electrodes and particles gain energy as they are attracted from one to the other. A magnetic field keeps them moving in a circular motion. Particles spiral out as they speed up.
What do synchrotrons consist of?
A very large circle of magnets and electrodes.
How does a synchrotron work?
Electromagnets keep particles moving in a circular path whilst they are accelerated by electrodes.
Give the range of speeds that can be achieved by a synchrotron.
500 GeV to several TeV.
Give one important consequence of special relativity.
No particle that has mass can move at a speed greater than or equal to the speed of light, c.
Taking into account relativistic effects, what happens as you increase the kinetic energy of a mass?
It gets more massive.
Give an equation to calculate the relativistic factor in terms of particle energies.
𝛾 = E total / E rest
What equation can you use to calculate the rest energy of a particle?
E rest = mc^2
Electrons in an atom can only exist in…
Discrete energy levels.
n = 1 represents which energy level of the electron?
The ground state.
How can electrons move down energy levels?
Emitting a photon.
Why can the wavelengths of photons emitted from atoms only take certain values.
Because the differences in energy levels are discrete.
Which energy level has a value of zero?
n = ∞
Why are electrons vaults used to measure energy levels in the atom?
The energy levels are very small.
What is the definition of an electron-volt?
The kinetic energy carried by an electron after it has been accelerated through a p.d. of 1 volt.
What is the value of one electron-volt in joules?
1.6 x 10^-19
What happens to the atom when an electron moves to an every level of zero?
It has become ionised.
Give the equation used to work out the frequency of a photon emitted when an electron moves from E1 to E2.
∆E = E2 - E1 = hf
Give the equation used to work out the wavelength of a photon emitted when an electron moves from E1 to E2.
∆E = E2 -E1 = hc/λ
What are fermions?
Particles that obey the Pauli exclusion principle.
What is the Pauli exclusion principle?
It states that no two fermions can exist in exactly the same quantum state at the same time.
What does Pauli’s exclusion principle mean in terms of energy levels of an atom?
No more than two electrons can be in the same energy level at the same time.
What do you get when light with a continuous spectrum passes through a cool gas?
A line absorption spectrum.
Why are line absorption spectrum produced when light travels through a gas?
Because photons of certain wavelengths are absorbed by the electrons to excite them to higher energy levels.
What does a line absorption spectrum look like?
A continuous spectrum with dark lines corresponding to the absorbed wavelengths.
What causes emission spectra?
Photons emitted by electrons moving to lower energy levels in an atom.
Compare emission and absorption spectra for the same atom.
The dark lines in the absorption spectrum correspond to the bright lines in the emission spectra.
Which model can be used to simplify energy levels of the atom?
Standing waves.
Why can the standing wave model be applied to electrons in an atom?
They both can only take discrete frequencies.
For a wavelength to be of the right energy level, it must…
Fit the circumference of the orbit a whole number of times.
What is the principal quantum number?
The number given to each energy level.
What is the principal quantum number in terms of the standing wave model?
The number of complete waves that fit the circumference or orbit.
Give the equation for each energy level of an electron in the different energy states of a hydrogen atom.
En = -13.6eV/n^2