Physics AS unit 1 (AQA) particle physics

Isotope- the same no. of protons and electorns, different no. of neutrons

specific charge= charge/mass

e.g. for a nucleus of hydrogen (one proton)

charge= +1.6x10^-19C mass= 1.67x10^-27 Kg

specific charge= +1.6x10^-19/1.67x10^-27 = 9.58x10⁷ C Kg^-1

strong nuclear force- the force that holds the nucleus together, it has an increadibly small range. It overcomes the electrostatic force that repels protons and neutrons.

Radio Active decay

Alpha decay consists of 2 protons and 2 neutrons- helium nucleus

Beta decay consists of a fast moving electron

Where a neutron changes into a proton and releases an electron and an anti neutrino.

Gamma radiation a form of electromagnetic radiation, has no mass or charge.

λ=c/f where c is the speed of light =3.0x10⁸

electromagnetic waves are emitted when a charged particle loses energy:

• a fast moving electron slows or stops
• an electron in a shell moves to a lower energy level

-emitted as bursts of energy, also known as 'photons'

E=h/f where h is planck's constant = 6.63x10^-34 Js

laser beams are just photons of the same frequency emitted at the same time.

power of a laser=nhf where n is the no. of photons per second

when matter and antimatter meet, they annhilate each other and emit 2 photons. The mass of the particles is converted into photons.

• every particle has an antiparticle with the exact same rest mass, but exact opposite charge.

Pair production is where a single photon creates a particle and antiparticle pair.

hf_min = E₀ where E₀ is the rest mass of each particle

hf_min = minimum photon energy

Weak nuclear force is how leptons interact and how hadrons decay, it is also how hadron-lepton interactions take place.

The weak nuclear force is represented by the W bosons, these have:

• non-zero rest mass (unlike photons)
• A very short range
• And a charge (W- , W+ )

Feyman diagrams represent an interaction between particles, the y-axis represents time.

Hadrons- Particles and antiparticles that interact through the strong interaction, e.g. protons, neutrons, K mesons

Leptons- Interact via the weak interaction

But all charged particles also interact via through electromagnetic waves.

Hadrons, also decay via the weak interactions

Hadrons

Baryons protons and all other hadrons that decay, directly or indirectly to protons. They are made of 3 quarks or 3 antiquarks

Mesons hadrons that don't include protons in their decay. made of one quark and one antiquark.

There are 3 different types of Mesons: electrons (e^-), Muon (μ), Tau (τ)

Each have their own neutrinos: ν_e, ν_μ, ν_τand they must each be counted seperatly so that lepton no. is always conserved.

In muon decay μ^- ---> e^- + ν_e + ν_μ

But not μ^- ---> e^- + ν_e + ν_μ

As lepton no. is not conserved

There are 3 types of Quarks- up (u), down (d), and strange, each with their corresponding antiquarks.

In the strong interaction strangness is always conserved.

u d s u d s

charge +2/3 -1/3 -1/3 -2/3 +1/3 +1/3

Strangness 0 0 -1 0 0 +1

stangness does not have to be conserved in the weak interaction

a baryon consists of 3 quarks, e.g proton= uud, antiproton=uud

a meson consists of a quark and an antiquark e.g K⁰ ds

1. Conservation of energy and charge

-applies to all science

2. Conservation of lepton no.

3. Conservation of Baryon no.

4. Conservation of strangness

5. Conservation of Quark no.

Photoelectric emission of electrons from a metal surface only takes place if the frequency of the incident electromagnetic radiation is above the value known as the threshold frequency (depends on the metal)

Einstien suggested light consists of wave packets, or photons.

Energy of photon=hf where his planck's constant = 6.63x10^-34 Js

An electron can leave the surface of the metal if the energy gained from a single photon exceeds the work function (ϕ) of the metal.

E_kmax =hf-ϕ where E_kmax is the max energy of the electron

hf=E_kmax +ϕ F_min=ϕ/h

An electron in a shell near the nucleus has less energy than one further away.

The lowest energy state of an atom is called its ground state, when an atom absorbs energy, one or more electrons move to a higher energy level. This means the atom is now in an excited state.

There are only discrete energy levels an electron can have.

When an electron de-excites, it emits a photon, for example in flourescent tubes, visible light is emitted.

When light is passed through a prism, it seperates out.

A line absorbtion spectra is formed when white light is passed through cold gas. it shows the whole spectra with a few black lines, this shows the atoms which have absorbed wavelengths of the white light.

A line emission spectra shows bright lines on a black background, these are the wavelengths emitted from the excited gas.

Light demonstrates both wave-like and particle-like nature.

Wave-like: diffraction of light when light is passed through a slit.

Particle like: Photoelectric effect

Electrons also show wave like nature. The wave-like behaviour is characterised by its wavelength, its De Broglie Wavelength (λ)

λ= h/mv h=planck's constant m=mass

v=velocity

Everything has a de broglie wavelength, so in theory everything can behave like a wave