Physics paper 1

Alpha decay

The process of an unstable nucleus emitting an alpha particle (2 protons 2 neutrons) to become more stable.

Annihilation

The process of a particle and its antiparticle colliding and being converted into energy- the energy is released in 2 photons to conserve momentum.

Antiparticle

All particles have a corresponding antiparticle with the same mass but opposite charge and conservation numbers.

Baryon

A class of hadron, that is made up of three quarks. The proton is the only stable baryon.

Baryon number

A quantum number that is conserved in all particle interactions.

Beta-minus decay

The process of a neutron inside a nucleus turning into a proton, and emitting a beta-minus particle (electron) and an antineutrino.

Beta-plus decay

The process of a proton inside a nucleus turning into a neutron, and emitting a beta-plus particle (positron) and a neutrino.

Electron diffraction

The spreading of electrons as they pass through a gap similar to the magnitude of their de Broglie wavelength- it is the evidence of wave like properties of particles.

Electron volt (eV)

The work done to accelerate an electron through a potential difference of 1V- 1eV is equal to the charge of an electron (E\=qv).

Energy levels

Defined and distinct energies at which electrons can exist in an atom- an electron can't exist between energy levels.

Excitation

The process of an electron taking in exactly the right quantity of energy to move to a higher energy level.

Gauge boson

The exchange particles that transmit the four fundamental interactions between particles.

Ground state

The most stable energy level that an electron can exist in.

Hadrons

A class of subatomic particle that experiences the strong nuclear interaction.

Ionisation

The process of an atom losing an orbital electron and becoming charged.

Isotope

Same number of protons but different number of neutrons.

Isotopic data

Data from isotopes that can be used for a purpose, such as carbon dating.

Kaon

A type of meson that decays into pions.

Lepton

A group of elementary subatomic particles, consisting of electrons, muons, and neutrinos.

Lepton number

A quantum number that is conserved in all particle interactions, both electron lepton numbers and muon lepton numbers must be conserved.

Meson

A class of hadron that is made up of a quark and antiquark pair.

Muon

A type of lepton that decays into electrons.

Neutrino

A subatomic particle whose existence was hypothesised to maintain the conservation of energy in beta decay.

Nucleon

A proton or neutron.

Nucleon number (A)

The sum of the number of protons and neutrons in a given nucleus.

Pair production

The process of a sufficiently high-energy photon converting into a particle and its corresponding antiparticle- to conserve momentum, it usually occurs near a nucleus.

Photon

A packet of energy.

Pion

A type of meson and the exchange particle for the strong nuclear force.

Positron

A positively charged particle that is the antiparticle of an electron.

Proton number (Z)

The number of protons present in the nucleus of a given element.

Stopping potential

The minimum potential difference required to stop the highest kinetic energy electrons from leaving the metal plate in the photoelectric effect.

Strange particles

Particles that are produced through the strong interaction but decay through the weak interaction.

Strangeness

A quantum number that is conserved in strong interactions but not in weak interactions- this reflects that strange particles are always produced in pairs.

Strong nuclear force

A force that acts between nucleons in a nucleus to keep it stable- it is attractive at distances of up to 3fm and repulsive at separations less that 0.5fm.

Threshold frequency

The minimum frequency of photons required for photoelectrons to be emitted from the surface of a metal plate through the photoelectric effect- it is equal to the metal's work function divided by Planck's constant.

Work function

The minimum energy required to remove an electron from a metal's surface.

Amplitude

A wave's maximum displacement from its equilibrium position.

Antinode

A position of maximum displacement in a stationary wave.

Cladding

A protective layer on an optical fibre to improve the tensile strength of the fibre, prevent scratching, and to prevent signal transfer between adjacent fibres.

Coherence

Waves are coherent if they have the same wavelength and frequency, as well as there being a fixed phase difference between them.

Diffraction grating

A grating with hundreds of slit per millimetre, that results in sharper interference patterns- they are used to calculate atomic spacing and to analyse elements.

Diffraction

The spreading of waves as they pass through a gap of similar magnitude to their wavelength.

Electromagnetic waves

Waves that consist of perpendicular electric and magnetic oscillations.

Frequency

The number of waves that pass a point in a unit time period- it is the inverse of the time period.

Fringe spacing

The distance between two adjacent bright fringes or two adjacent dark fringes.

Interference

The name given to the superposition of waves that occurs when two waves meet- if the waves are in phase they will constructively interfere, but if they are out of phase, they will destructively interfere.

Laser

A light source that produces a collimated and coherent beam.

Longitudinal wave

A wave with oscillations that are parallel to the direction of energy propagation (e.g. sound waves).

Material dispersion

Waves of different wavelengths travel at slightly different speeds through an optical fibre and so reach the end of the fibre at slightly different times, causing pulse broadening- the use of monochromatic light fixes this.

Modal dispersion

Waves enter an optical fibre at slightly different angles, meaning the distance each beam has to travel is slightly different- this leads to the beams reaching the end at different times and so causes pulse broadening.

Node

A position of minimum displace in a stationary wave.

Optical fibre

A thin glass fibre through which signals are passed through.

Path difference

A measure of how far ahead a wave is compared to another wave, usually expressed in terms of the wavelength.

Phase difference

The difference in phase between two points on a wave- usually expressed in radians.

Phase

A measure of how far through the wave's cycle a given point on the wave is.

Polarisation

The restriction of a wave so that it can only oscillate in a single plane- this can only occur for transverse waves.

Pulse broadening

The elongation of a signal passed down an optical fibre, commonly due to modal or material dispersion.

Refractive index

A material property that is equal to the ratio between the speed of light in a vacuum, and the speed of light in a given material.

Snell's law

A law linking a wave's angle of incidence to its angle of refraction, with the use of the refractive indexes of the mediums involved.

Speed

The product of a wave's frequency and wavelength.

Stationary wave

A wave that stores, but doesn't transfer, energy.

Total internal reflection

An effect that occurs in optical fibres, where full reflection occurs at the inside boundary of the fibre, meaning no radiation passes out.

Transverse wave

A wave with oscillations that are perpendicular to the direction of energy propagation (e.g. EM waves).

Wavelength

The distance between two identical positions on two adjacent waves- it is commonly measured from peak to peak or trough to trough.

Young's double-slit experiment

An experiment that demonstrates the diffraction of light by passing monochromatic light across two narrow slits and observing the resulting pattern of bright and dark fringes.

Breaking stress

The maximum stress that an object can withstand before failure occurs.

Brittle

A brittle object with show very little strain before reaching its breaking stress.

Centre of mass

The single point through which all the mass of an object can be said to act.

Conservation of energy

Energy can't be created or destroyed- it can only be transferred into different forms.

Conservation of momentum

The total momentum of a system before an event, must be equal to the total momentum of the system after the event, assuming no external forces act.

Couple

Two equal and opposite parallel forces that act on an object through different lines of action- it has the effect of causing rotation without translation.

Density

The mass per unit volume of a material.

Efficiency

The ratio of useful output to total input for a given system.

Elastic behaviour

If a material deforms with elastic behaviour, it will return to its original shape when the deforming forces are removed- the object won't be permanently deformed.

Elastic collision

A collision in which the total kinetic energy of the system before the collision is equal to the total kinetic energy of the system after the collision.

Elastic limit

The force beyond which an object will no longer deform elastically, and instead deform plastically- beyond the elastic limit, when the deforming forces are removed, the object won't return to its original shape.

Elastic strain energy

The energy stored in an object when it is stretched- it is equal to the work done to stretch the object and can be determined from the area under a force-extension graph.

Equilibrium

For an object to be in equilibrium, both the resultant force and resultant moment acting on the object must be equal to zero.

Hooke's law

The extension of an elastic object will be directly proportional to the force applied to it up to the object's limit of proportionality.

Impulse

The change of momentum of an object when a force acts on it- it's equal to the product of the force acting on the object and the length of time over which it acts.

Inelastic collision

A collision in which the total kinetic energy of the system before the collision isn't equal to the kinetic energy of the system after the collision.

Moment

The product of a force and the perpendicular distance from the line of action of the force to the pivot.

Momentum

The product of an object's mass and velocity.

Newton's first law

An object will remain in its current state of motion, unless acted on by a resultant force- an object requires a resultant force to be able to accelerate.

Newton's second law

The sum of the forces acting on an object is equal to the rate of change of momentum of the object.

Newton's third law

Every action has an equal and opposite reaction- if an object exerts a force on another object, then the other object must exert a force back, that is opposite in direction and equal in magnitude.

Plastic behaviour

If a material deforms with plastic behaviour, it won't return to its original shape when the deforming forces are removed- the object will be permanently deformed.

Principle of moments

For an object to be in equilibrium, the sum of the clockwise moments acting about a point must be equal to the sum of the anticlockwise moments acting about the point.

Scalar

A scalar quantity is one that only has a magnitude (e.g length, mass, tempurature).

Spring constant

The constant of proportionality for the extension of a spring under a force- the higher the spring constant, the greater the force needed to achieve a given extension.

Stiffness

A measure of how difficult it is to stretch a given object.

Tensile strain

The ratio of an object's extension to its original length, it is a ratio of two length and so has no unit.

Tensile stress (Pa)

The amount of force acting per unit area- its unit is the pascal.

Terminal speed

The maximum speed of an object that occurs when the resistive and driving forces acting on the object are equal to each other.

Vector

A vector quantity is one that has both a magnitude and a direction (e.g. velocity, displacement, acceleration).

Young modulus (Pa)

The ratio of stress to strain for a given material- its unit is the pascal.

Ammeter

A device that measure the current in the loop of the circuit that it's connected in series with- an ideal ammeter is modelled to have zero resistence.

Current

The rate of flow of charge in a circuit.

Electromotive force

The amount of energy transferred by a source, to each unit of charge that passes through it.

Internal resistance

The resistance to the flow of charge within a source- internal resistance result in energy being dissipated within the source.