Physics

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Atomic Structure & Stable and Unstable Nuclei

Isotopes have a different number of neutrons, but the same amount of protons. This affects the stability of the nucleus, unstable nuclei may become radioactive and decay into more stable.

The specific charge is the charge of a particle over its mass. ((proton number or - ion number x 1.6x10^-19) / (nucleon number x 1.67x10^-27))

The strong nuclear force binds nucleons together, it overcomes the electrostatic repulsive force. It has a very short range of a few femtometres 1fm = 1x10^-15. The force works equally between all nucleons. At very small separations, the strong nuclear force must be repulsive or it would crush the nucleus.

An alpha particle has two protons and two neutrons.

In beta minus decay a particle gains an electron, as the proton number increases by one, but the nucleon number stays the same as a neutron is lost, also a neutral particle called an antineutrino is released.

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Particles and Antiparticles & Forces and Exchange

Photons and are packets of em radiation E = hf = hc/λ.

Pair production is where a particle and antiparticle are produced from a gamma ray, usually you get an electron-positron collision as they have a low mass. The min. energy = the total rest energy.

The opposite of this is annihilation where the meeting of a particle and an antiparticle collison resides in the mass being converted into energy, producing two gamma ray photons shooting off in opposite directions.

An em interaction has a virtual photon as its exchange particle, where only charged particles are affected. A weak interaction has W+&- bosons as its exchange particles and affects all types of particles. A strong interatcion has pions as the exchange particles between nucleons and affects hadrons only, gluons are exchanged between quarks. Gravity only matters with big masses like stars and planets as it is so feeble.

The larger the mass of the gauge boson (exchange particle), the shorter the range of the force.

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Forces and Exchange Particles Pt. 2 & Classificati

Feynman diagrams are useful to show particle interactions. An electron proton collision is shown. Only hadrons can feel the strong force, hadrons aren't fundamental, they're made of quark

(http://www.cyberphysics.co.uk/graphics/diagrams/Feynman/Feynmanepcollision.gif)Hadrons are baryons and mesons. Baryons are protons (only stable), neutrons and sigma (not in normal matter) particles. They all decay to a proton. Mesons have baryon no. 0 and are pions and kaons. There are loads of lightest mesons pions in high-energy collisons like CERN. Kaons are heaviest mesons and more unstable, very short lifetime and decay to pions. Mesons interact with baryons via strong force.

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Classification of Particles Pt. 2 & Quarks Pt. 1

Leptons (electrons and neutrons etc.) don't feel the strong force. Only interact with other particles via the weak force (along with a bit of gravitational and em if charged). Electron is stable, muon = heavy electron. Muons are unstable and decay into electrons. Electron & muon have their own neutrino, ve & vu,. Neutrinos only take part in weak interactions, they have 0 charge and almost 0 mass. Can pass through earth without it being impacted.

Lepton no. for muon and electron, Lu & Le. e.g. antimuon charge +1, Le 0, Lu -1.

Quarks building blocks for hadrons, up (u), down (d) and strange (s) if particle has strangeness. Strange = Kaons, created via strong, decay weak. Strangeness conserved in strong, not in weak. Strange particles always produced in pairs, e.g. K+ & K-. Quarks & antiquarks opposite properties like antiparticles (opposite baryon, charge and strange number).

Baryons - 3 quarks. Mesons - quark & antiquark.

Weak can change quark type, B- decay, neutron -> proton (uud -> udd), (d->u in weak overall). Unstable decay by B+ decay proton -> neutron (udd -> uud), (u->d unstable weak overall.

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Quarks Pt. 2

Properties conserved in particle interactions are charge, baryon number, strangeness in strange interactions and lepton number. Although for lepton no. the different types have to be calculated differently, e.g. Le & Lu. E.g. Pion- -> u- + antiv-u, this can happen as for Lu 0 -> 1 + -1. An interaction that would not happen would be e- + ve -> u- as for Le 1 + 1 -> 0, and for Lu 0 -> 1.

No such thing as a free quark. Can't separate quarks, energy = more quarks, pair production.

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EM Radiation and Quantum Phenomena - Photoelectric

If you shine light of a high enough frequency onto the surface of a metal, the metal will emit electrons, for most, the frequency falls in the UV range. The free electrons on the surface absorb energy from the light, and if the electron absorbs enough energy, the bonds holding the electron to the metal will break to release it. The electrons emitted are called photoelectrons.

Einstein suggested that EM waves and the energy they carry exist in packets called photons.    E = hf = (hc)/Λ is the equation, where E = the photon energy. When a metal surface is bombarded by photons, if an electron collides with the photon then it will gain energy = to hf.

To break the bonds before leaving, an electron will need to exceed the energy called the work function, this value will depend on the metal. The metal will heat up if the energy gained is < the work function and will be emitted if the energy is > the work function. As hf >/= wf, f = (wf/h).

The kinetic energy is what the electron carries when it leaves the metal minus any energy lost on the way out. Electrons deeper down lose more energy, leading to a range of energies.

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Photoelectric Effect Pt.2 & Energy Levels and Phot

The minimum amount of energy an electron can lose in its emitting stage is the work function. So hf = wf + Ek(max) where Ek(max) = 0.5m(vmax^2). The ek is independent of the intensity.

The stopping potential gives the maximum kinetic energy. The emitted electrons are made to lose their energy by doing work against an applied p.d.. The stopping potential Vs is the p.d. needed to stop the fastest moving electrons with Ek(max).

eVs = Ek(max). e=1.6x10^-19C, Vs = stopping potential in V, and Ek(max), measured in J. 1eV = 1.6x10^-19 J.

Change in E = E2 - E1 = hf. Energy gained by electron (eV) = accelerating voltage (V).

n = 1 is the ground level. Electrons move down an energy level by emitting a photon and move up by absorbing a photon, the latter is called excitation. 

The spectrum of white light is continuous.

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