AQA A-Level Physics Particles

What is a nucleon

a proton or neutron in a nucleus

Why does the electron orbit the nucleus

This is because the electron has negative charge and the nucleus is positively charged because of protons, so electrons attracted by electrostatic forces of attraction.

charge of electron

-1.6 x 10^-19 C

charge of proton

1.6 x 10^-19 C

mass of electron

9.11 x 10^-31 kg

mass of proton and neutron

1.67 x 10^-27 kg

atomic number

the number of protons in the nucleus of an atom

mass number

the sum of the number of neutrons and protons in an atomic nucleus

Isotopes

Atoms of the same element that have different numbers of neutrons

Nuclide

a general term for a specific isotope of an element

Specific charge

The charge per unit mass of a particle

Example of specific charge calculation on sodium ion

A sodium ion has a mass of 23 proton masses (mp).

This is 3.85 × 10-26kg.

It also has a charge of +1 electron charges (e).

This means its charge is 1.60 × 10-19C.

So:

Specific charge = (1.60 × 10-19C) ÷ (3.85 × 10-26kg)

Specific charge = 4.16 × 106C/kg

strong nuclear force

a powerful force of attraction that acts only on the neutrons and protons in the nucleus, holding them together

What force does the strong nuclear force overcome

Overcomes the electrostatic forces of repulsion between protons in the nucleus

Range of strong nuclear force

0.5-3fm. Repulsion below 0.5fm

Is the effect of strong nuclear force the same between 2 protons as it is between a proton and a neutron or 2 neutrons

Yes

What happens below 0.5 fm

The strong nuclear force becomes a resistive force acting to prevent neutrons and protons being pushed into each other

What makes a nucleus unstable

too many or too few neutrons relative to the number of protons

How do nuclei with too many nucleons decay

Alpha decay (emission of a helium nucleus formed of 2 protons and 2 neutrons).

How do nuclei with too many neutrons decay

Beta minus decay in which a neutron decays to a proton by the weak interaction (quark character has changed from udd to uud)

Beta minus decay equation

neutron -> proton + beta - particle + antineutrino

Beta plus decay equation

proton -> neutron + positron + neutrino

How was existence of neutrino hypothesised

The energy of particles after beta decay was lower than before, a particle with 0 charge (to conserve charge) and negligible mass must carry away this excess energy, this particle is the neutrino.

What is a photon

a particle of electromagnetic radiation having zero mass and carrying a quantum of energy

How does a photon behave

It can behave as a particle or a wave

_____ of a photon is directly proportional to _________

Energy of a photon is directly proporional to frequency

Equation of energy

E=hf where h = Planck's constant

Value for Planck's Constant

6.63 x 10^-34 Js

In what planes does an electromagnetic wave oscillate

They oscillate in multiple planes.

When are electromagnetic waves emitted from charged particles?

When they lose energy

Give 2 examples of this occurring

fast-moving electron is stopped, changes direction, slows down

Electron in shell of an atom moves to different shell of lower energy

How are EM waves emitted

Electromagnetic waves are emitted as short bursts of waves, each burst leaving the source in a different direction. Each burst is a packet of electromagnetic waves and is referred to as a photon.

A laser beam contains ______ of the same _________

A laser beam contains photons of the same frequency

Power of a Beam Equation

p=nhf for n number of photons

Important equations

W=QV E=hf f=c/wavelength

electron volt

An energy unit, particularly for atomic and nuclear processes, is the energy given to an electron by accelerating it through 1 volt of electric potential difference.

Electron volt to Joules conversion

1.6 x 10-19 joules.

What is an antiparticle

For each particle there is an antiparticle with the same rest energy and mass but all other properties are the opposite of its respective particle. Have equal but opposite charge.

Does every particle have an antiparticle

Yes

Do untable particles and antiparticles have same lifetime

Yes

What occurs when a particle and antiparticle meet

Annihilation:

The mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which go in opposite directions to conserve momentum.

What is pair production

This is where energy is converted into mass and you get equal amounts of matter and antimatter. This only happens if there is enough energy to produce the total rest masses of the particles. It must always produced a particle and corresponding antiparticle as certain quantities have to be conserved.

Minimum energy of photon needed=

hf(min)=2E(0)

where f(min) is minimum photon frequency required. E(0) is rest mass energy of particles

4 fundamental forces

electromagnetic, strong nuclear force, weak nuclear force, gravitational force

4 fundamental forces ranked by strength

1) strong nuclear force

2) electromagnetic force

3) weak nuclear force

4) gravitational force

what are exchange particles

virtual particles which are responsible for how forces act between two particles

Exchange particle for electromagnetic force

Virtual photon

Exchage particle for strong nuclear force

Gluon (inside nucleons) and meson (between nucleons)

Exchange particle for weak nuclear force

W + and - bosons

Exchange particle for gravitational force

graviton

Why are exchange particles virtual?

Because they cannot be detected directly

fennyman diagram

What does the electromagnetic force act on

All charged particles

Feyman diagram for electromagnetic force

Why is the weak nuclear force weaker than strong nuclear force

As it does not affect stable nuclei and only affects unstable nuclei

What fundamental force is involved in beta decay

weak nuclear force in beta + and - decay

What exchange particle is used in beta + and - decay

W+ bosons for beta + decay

W- bosons for beta- decay

Neutron neutrino interaction

Proton antineutrino interaction

W-bosons and photons differences

W-bosons have non-zero rest mass

W-bosons have very short range of no more than 0.001 fm

W-bosons are positively charged or negatively charged.

Beta - decay

W- boson decays into beta - particle and antineutrino

Beta + decay

W+ boson decays into beta + particle and neutrino

electron capture

Proton in proton-rich nucleus turns into neutron as result of interacting through weak interaction with inner shell electron.

What does W+ boson do in electron capture

Turns electron into neutrino

What types of particles are affected by strong nuclear force

Hadrons

the antiparticle to the proton is the

antiproton

charge of antiproton

-1

interactions the proton undergoes

strong, weak, electromagnetic

antiparticle of neutron

Antineutron

interactions neutron undergoes

strong, weak

why does neutron not undergo electromagnetic force

Because it is not charged

Interactions neutron undergoes

strong, weak forces

antiparticle of electron and it's charge

positron, +1

interactions electron undergoes

weak, electromagnetic

neutrino charge and antiparticle

0, anti-neutrino

muon charge and antiparticle

-1, anti-muon (charge +1)

What charge can pions have?

They can be positive, negative, or neutral.

What do pions decay into?

Muons, antimuons and neutrinos.

What forces do pions interact via?

Strong, weak and electromagnetic forces

What types of charge can kaons have?

They can be positive, negative, neutral, or anti-neutral.

What do kaons decay into?

Pions.

What types of forces do kaons undergo?

Strong and electromagnetic forces.

What do muons decay into

Muons decay into electrons, neutrinos and anti-neutrinos.

Hadrons

Particles that are affected by strong nuclear force, and contain quarks

How do hadrons tend to decay

through weak interaction

What are leptons?

Leptons are one of the classes of fundamental particles.

Can leptons be broken down into smaller particles?

No, leptons cannot be broken down into smaller particles.

Name four types of leptons.

Electrons, muons, tauons, and neutrinos.

How do leptons interact

Via the weak interaction

Energy of particles before collision

Total energy of particles and antiparticles before= rest energy + kinetic energy

Energy of particles after collision

rest energy+ kinetic energy

Baryons

Hadrons which contain 3 quarks, including protons and neutrons

Mesons

Subatomic particles made of quark-antiquark pairs

What happens when lepton and antilepton collide

Produce quark and antiquark

What happens in an interaction between lepton and hadron

neutrino/antineutrino can change into or from a corresponding charged lepton

Lepton number of leptons and antileptons

+1 for all leptons

-1 for all antileptons

What happens in muon decay

-Muon changes into a muon neutrino. An electron is created to conserve charge and a corresponding anti neutrino is created to conserve lepton number.

quark properties

In what number are strange particles created

In twos

What does a kaon decay into?

2 pions