1 Joel Biffin

AS Physics

Unit 1: Particle, Quantum Phenomena & Circuits

Joel Biffin

2 Joel Biffin

Particles & Radiation [1.1]

Quantum Phenomena [1.2]

Electricty [1.3]

Unit 1: Particles, Quantum & Electricity Particles & Radiation [1.1]

3 Joel Biffin

Unit 1 | Particles & Radiation [1.1] Inside the Atom

- An atom is made up of a nucleus of protons and neutrons surrounded by electrons.

Stable & Unstable Nuclei

- The strong nuclear force (S.N.F.) overcomes electrostatic repulsion between protons and holds nucleons together.

- The S.N.F. has a range of +3fm (3x10-15m).

- Atoms can decay radioactively by the following equations:

> Alpha Decay

> Beta (-) Decay

> Beta (+) Decay

Quarks & Particle Classification

- Quarks are a type of fundamental particle which can join together to create Hadrons.

- There are 3 different quarks (and 3 corresponding anti-quark) - Up, Down & Strange.

- Hadrons interact via the strong force (and decay via the weak force in strange interactions).

Particle Name Charge Mass

Relative Actual /C Relative Actual /kg

Proton +1 1.60x10-19 1 1.67x10-27

Neutron 0 0 1 1.67x10-27

Electron -1 -1.60x10-19 5.45x104 9.11x10-31

Unit 1: Particles, Quantum & Electricity Particles & Radiation [1.1]

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- Different combinations of quarks form different types of Hadrons:

> Baryons - they contain 3 quarks (and have a baryon number of 1 or -1)

> Mesons - they contain 1 quark and 1 anti-quark and can be either Pions or Kaons

~ Pions contain only up or down quarks/antiquarks ~ Kaons always have one strange quark/antiquark

- Leptons are fundamental particles with a very small mass.

- There are three different types of lepton:

> Electrons, Muons & Neutrinos (Electron-Neutrinos & Muon-Neutrinos).

Interactions Involving Particles, Anti-Particles & Photons

- For each particle, there is a corresponding anti-particle (e.g. Electron (e-) - Positron (e+)).

- When particles interact, exchange particles (gauge bosons) are the force particles which are exchanged between bodies to produce the force.

> Electromagnetic Force - (Virtual) Photon

> Weak Force - W+ or W-

> Strong Force - Gluon

> Gravitational Force - Gravitron / Higgs-Boson

- We can illustrate how particles interact by using Feynman diagrams.

Electromagnetic Repulsion

Electron Capture

Unit 1: Particles, Quantum & Electricity Particles & Radiation [1.1]

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Neutron - Neutrino Collision Antineutrino - Proton Collision

Electron - Proton Collision Beta- Decay

Definitions

Specific Charge The charge (in coulombs) divided by the mass (in kg). Sometimes referred to as the charge to mass ratio

Isotope A nucleus with the same number of protons but with a different number of neutrons

Unit 1: Particles, Quantum & Electricity Quantum Phenomena [1.2]

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Unit 1 | Quantum Phenomena [1.2] The Photoelectric Effect

- The process by which electrons are emitted from the surface of a metal due to incident light of an appropriate frequency is called the photoelectric effect.

Collisions of Electrons with Atoms

- Ionisation occurs when electrons with a high level of kinetic energy hit gaseous atoms - the electrons have such a high energy that they knock out an electron from the incident atom.

- Excitation occurs when electrons with kinetic energy collide with atoms - upon collision, the incident electron transfers its energy to the atom, allowing an electron inside the atom to move to a higher energy level.

- De-excitation occurs following excitation, when the excited atom needs to lose energy - the excited electron moves to a lower energy level emitting characteristic electromagnetic radiation (spectra) due to energy conservation laws.

- The spectra that are produced when an atom de-excites support the fact that there are discrete energy levels in an atom as the spectra produced help to show the distance (energy change) between energy levels.

- The energy of the emitted photon, following de-excitation, is shown by the following:

Wave-Particle Duality

- When an electron beam is fired at metal foil the electrons are diffracted by the foil - this is an example of particles behaving in a wave-like nature.

- The photoelectric effect is an example of waves behaving in a particle-like nature as the energy is absorbed from incident light.

- The de Broglie equation for wavelength allows us to compare particle properties and wave properties in order to make calculations using a mixture of data types.

Unit 1: Particles, Quantum & Electricity Quantum Phenomena [1.2]

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Definitions

Photoelectric Effect The emission of electrons from metal surfaces by incident light of an appropriate frequency

Work Function The minimum energy required for an electron to escape from the surface of the metal

Threshold Frequency The minimum frequency of a photon to produce photoelectrons

Electron Volt (eV) The energy given to an electron as it passes through a p.d. of 1 volt

Ionisation Energy of an Atom

The minimum energy required to remove an electron from an atom in its ground state

Excitation Energy The energy required to move an electron from a lower energy level to a higher energy level

Line Spectra The characteristic wavelengths of light produced by individual excited atoms

Unit 1: Particles, Quantum & Electricity Electricity [1.3]

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Unit 1 | Electricity [1.3] Current & Potential Difference

- Electric current is the flow of charge per unit of time.

- Potential Difference is the work done per unit of charge from one point to another.

Resistance & Resistivity

- Resistance is the potential difference across a component divided by the current going through it.

- In a filament lamp, when the temperature increases (i.e. higher current) there is a higher resistance due to more vibration in its particles.

- In a semiconductor diode, the resistance is infinite until the p.d. across the diode reaches 0.7V the diodes resistance falls rapidly

- The resistivity of a material is a measurement of how the material works as a resistor.

- Superconductors are materials that at (or below) a certain temperature have a resistivity of zero.

- Superconductors can be very useful in making strong magnets.

Potential Divider

- The potential divider can be used to change the voltage supply in a circuit.

> Can be used in volume controls, for example.

Unit 1: Particles, Quantum & Electricity Electricity [1.3]

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Electromotive Force (E.M.F.) & Internal Resistance

- E.M.F. is the energy supplied to a charge as it passes through a cell.

- Internal resistance is found in power supplies when the chemical reactions inside the cell do not happen instantaneously there are lost volts across the internal resistance which reduces the terminal voltage of the power supply.

Definitions

Electric Current The number of coulombs of charge passing a point every second

Potential Difference The work done per unit charge in moving charges from one point in the circuit to another

Resistance The ratio of the potential difference across a component to the current through it

Ohmic Conductor/Resistor

The ratio of the potential difference to current remains constant

Ohms Law The current through a component is proportional to the potential difference across it

Critical Temperature The temperature at(/below) which the resistivity of a superconductor becomes zero

Kirchoffs 1st Law The sum of the currents into a junction is zero

Kirchoffs 2nd Law In any closed loop, the sum of the EMF equals the sum of the p.d.

E.M.F. The total energy supplied (per coulomb) given to charges as they pass through the cell

Internal Resistance The resistance inside a component which supplies power (e.g. Battery/Cell)

Useful Volts The p.d. across the terminals of the power supply

Lost volts The p.d. across the internal resistance of the power supply

Time Base The control on an oscilloscope which changes the time it takes for the beam to cross the screen horizontally

Y-Gain The control on an oscilloscope which changes the sensitivity of the vertical voltage scale