physics alevel 1.1

Describe the formation of an atom.

Inside every atom, there is a nucleus containing protons and neutrons, known as nucleons. Electrons orbit the nucleus in shells

What is the relative charge and mass of the subatomic particles?

Protons: Charge +1 , Mass 1

Neutrons: Charge 0 Mass 1

Electrons Charge -1 Mass 0.0005

Describe the proton number.

Sometimes called the atomic number, has symbol Z.

No two elements have the same number of protons.

In a neutral atom electrons = protons.

Num of electrons tell us the chemical behaviours so proton number tells us about chemical properties

What are isotopes?

Atoms with the same number of protons but different number of neutrons.

What is the nucleon number ?

Mass number, has a symbol A (top).

how many protons and neutrons are in the nucleus.

What can we use Radioactive isotopes for?

Used to find how old sum is.

All living things contain same percentage of radioactive carbon-14 from atmosphere

After they die, carbon-14 decreases and decays to stable elements.

Scientists calculate approximate age of object containing organic matter by using isotopic data to find percentage of radioactive carbon-14 left in the object

What is a fundamental particle?

Particle that can’t break up into anything smaller.(no quarks)

Define Isotopic data

The relative amounts of different isotopes of an element present within a substance.

Define the calculation for isotopic data

relative atomic mass of a sample can be calculated by:

(Isotope num x (percentage abundance / 100))

What is the strong nuclear force?

To hold nucleus together, must be attractive force stronger than electrostatic.

Very short range, attractive up to 3fm, repulsive under 0.5fm / would crush the nucleus to a point

Electrostatic vs Strong Force

Repulsive electrostatic force between protons has larger range than strong nuclear forces

Electrostatic force influenced by charge and strong nuclear isnt

strength of strong nuclear force is the same between all types of nucleon

Define Unstable nuclei.

Too many protons, neutrons or both

will decay to become more stable

Type of decay depends on amount of nucleon in them

Describe Alpha decay.

Alpha decay only occurs with large nuclei

nuclei too massive for strong nuclear force to keep stable

When alpha particle emitted:

Proton number decrease by 2 (B) , nucleon number decrease by 4 (T)

Properties of Alpha particles?

Have very short range - few cm in air.

Can be observed by cloud chamber / or Geiger counter

Describe Beta-minus decay.

emission of an electrons from nucleus with antineutrino

Occurs in isotopes that are unstable due to being ‘neutron rich’

proton num increases by 1 (B), nucleon num stays the same

Equation for \beta^{-} decay?

n = p + e- + ve-

Equation for \beta^{+} decay ?

p = n + e+ + Ve

Explain the observation of neutrinos.

energies of other particles after beta decay was less than it was before which didn’t fit with conservation of energy.

1930 Wolfgang Pauli suggest another particle was being emitted, carrying missing energy,

Had to be neutral (or charge wouldn’t be conserved in beta decay)

Has zero or almost zero mass (never detected)

What forces are there in the nucleus?

Repulsive electrostatic force between protons due to positive charge

Attractive gravitational forces due to mass of nucleons

Explain why the strong nuclear force must be repulsive at very short distance?

Must be repulsive at very small nucleon separation to prevent nucleus from being crushed to a point

Explain why a nucleus contains two protons is unstable but one containing two protons and two neutrons is stable.

The protons repel each other with an electrostatic force and attract each other with nuclear strong force.

Strong force is not large enough to overcome this repulsion.

Two neutrons attract each other and protons via strong force now able to balance out the repulsion between the protons.

What is Electromagnetic radiation?

Electromagnetic radiation travels in packets called photons, which transfer energy and have no mass.

Energy of photons is directly proportional to frequency of electromagnetic radiation.

State the equation for electromagnetic radiation.

E = hc = hc/\lambda

h = 6.63 × 10^-34 J

c = 3.00 × 10^8 ms^-1

State the difference between a particle and antiparticle.

For every type of particle there is an antiparticle, same rest energy, mass but opposite charge

(amongst other things)

Describe the relations between mass and energy.

You can create matter and antimatter from energy.

When energy is converted into mass you get equal amounts of matter and antimatter.

What is pair production?

a photon is converted into an equal amount of matter and antimatter.

Can only occur when the photon has an energy greater than the total rest energy of both particles.

Any excess particles Is converted into kinetic energy

What is the process of annihilation?

When a particle meets its antiparticle = annihilation.

All the mass of particle and antiparticle gets converted back to energy

This energy along with kinetic energy is released in the form of 2 photons moving in opposite directions in order to conserve momentum.

What’s the definition of annihilation?

The destruction of a particle-antiparticle pair when they collide and covert their mass into gamma ray photons.

(two most common:

protons-antiproton annihilation

electron-positron annihilation

What’s the definition of pair production?

the creation of a particle-antiparticle pair when a high energy photon spontaneously converts its energy into mass.

What is an exchange particle?

Forces between particles are caused by exchange particles.

Exchange particles are virtual particles - only exists for a short period of time and not directly detectable.

carry energy and momentum between particles experiencing the force.

What are the four fundamental forces?

• Electromagnetic

• Weak

• Strong

• Gravity

Describe the fundermental forces.

• Electromagnetic:

virtual photon charged particles effected only.

• Weak:

W^+, W^-  All types of particles effected

• Strong:

pions, hadrons only effected

What is the weak nuclear force responsible for?

Beta decay, electron capture, electron-proton collisions

What is the relative strength and ranges of the fundermental forces?

Strong: 1

Electromagnetic: 10^-2

weak: 10^-6

gravity 10^-39

Draw and describe electromagnetic repulsion.

When two particles with equal charges get close, they repel

Draw and describe electron capture and proton capture.

Draw and describe beta plus and beta minus decay.

What are hadrons?

formed from quarks.

experience strong nuclear force, aren’t fundermental particles.

• Two types of hadrons: 

Baryons (3 quarks)

Mesons (quarks, antiquark)

What are the most common Hadrons and Mesons

Baryons: protons, neutrons

Mesons: pions, koans

What are the classes of anti-hadrons?

• Anti-baryons (3 quarks)

• Anti-mesons (quark and anti-quark pair)

What is the properties of baryons?

All baryons except protons are unstable.

They decay to become other particles.

Baryon num = +1

Anti-baryon num= -1

Baryon num is a quantum number and must be conserved.

Describe mesons.

Pions and kaons were discovered in cosmic rays.

All mesons are unstable and have a baryon number of B=0

• Koans:

heavy, unstable and can decay into pions.

Decay through the weak interaction.

• Pions:

can be +, -, 0 and is the exchange particle via the strong nuclear force.

Pions are the lightest meson, there are loads of pions in high energy particle collisions = CERN particle collider.

Describe leptons.

electron, muon, electron neutrino, muon neutrino.

Leptons are fundermental particles. (not made up of any other particles, no quarks)

Do not experience the strong nuclear force

electrons and muons both have a charge of -1

Describe the lepton number.

Its a quantum number that is conserved.

Leptons: +1

Anti-leptons: -1

Non-Leptons: 0 (baryons and mesons)

Describe muons. (Leptons)

muons are leptons that are heavier than an electron

typically decay into an electron, anti-muons decay into a positron.

Muon decay occurs through the weak interaction. (W^- Boson)

Describe strange particles.

Strange particles are particles that are produced through the strong interaction and decay through the weak interaction (eg kaons).

strange particles are always created in pairs.

strangeness in conserved in every interaction but the weak.

S: -1

S-: 1

Explain why a muon is not a meson.

Meson are hadrons, muon is a lepton.

The muon is a fundermental particle but mesons are not.

Mesons interact via strong force but mesons do not.

What properties must be conserved in particle interactions?

• Charge

• Baryon

• Energy and momentum

• Electron lepton number

• Strangeness is conserved in strong interaction.

Describe the process when a positron collides with a lepton.

Annihilation

Gamma photons are produced.

Lepton is an electron.

Explain which of the fundermental interactions is responsible for decay of neutron

weak nuclear interaction

it involves leptons

there is a change in quark

using the concept of exchange particles, why do electrons pathway change?

Exchange particles are virtual photons and have momentum.

Conservation of momentum enables pathway to change.

Explain how a third particle is produced during B- decay.

Third particle must be produced for conservation of energy.

Missing energy carried of by third particle

Describe the charges and Lepton numbers of Leptons.

Name.                      Charge.        Le.        Lu

Electron.                     -1.              +1.         0  

Electron-neutrino.        0.              +1.         0

muon.                          -1.              0.         +1

muon-neutrino.             0.              0.          -1

What is threshold frequency?

minimum frequency of light required for an electron to be emitted.

What is the photoelectric effect?

Where photoelectrons are emitted from the surface of a metal after light above a certain frequency is shown on it.

What’s the definition of photoelectron?

electrons that have been emitted from the surface of a metal plate by light

What are the 3 conclusion of the photoelectric effect?

no photoelectrons are emitted if the radiation has a frequency below a certain value

(threshold frequency)

Photoelectrons are emitted with a variety of kinetic energies ranging from zero to some max value.Value of max KE increases with frequency but unaffected with intensity

Num of photoelectrons emitted per second is proportional to the intensity of radiation.

What is threshold wavelength?

The longest wavelength of incident electromagnetic radiation that would remove electrons from the surface of a metal.

What’s the definition of work function?

The minimum energy required to release a photoelectron from the surface of a metal.

What is excitation?

When an electron absorbs enough energy to overcome to a high energy level.

What is ionisation?

when an atom gains or loses an orbital electron and becomes charged