Physics EA

Centripetal acceleration

the acceleration experienced by any object moving in a circular path directed towards the centre of motion

Centripetal force

the force acting on an object travelling in a circle that constantly either pulls or pushes the object in towards the centre of motion

Tangential velocity

The instantaneous velocity of an object in circular motion, directed tangent to the circular path and perpendicular to the radius

Law of Universal Gravitation

the force of attraction between each pair of point particles that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them

Universal gravitational constant, G

6.67×10^-11

Gravitational field

the region of space surrounding a body in which another body experiences a force of gravitational attraction

Gravitational field strength

the net force per unit mass at a particular point in the gravitational field

Gravitational field lines

Imaginary lines representing a gravitational field. Their direction shows the force on a test mass and their density represents field strength

Orbital velocity

The tangential velocity required for an object to maintain a particular orbit

Kepler's First Law

Planets move in elliptical orbits, with the Sun at one focus

Kepler's Second Law

A line joining a planet and the Sun sweeps out equal areas in equal time intervals

Kepler's Third Law

The square of an orbital period is proportional to the cube of the orbit's semi-major axis

Escape velocity

The minimum initial speed required for an object to escape a body's gravitational field without further propulsion

Coulomb's Law

a law stating that like electric charges repel and opposite electric charges attract, with a force proportional to the product of the electric charges and inversely proportional to the square of the distance between them

Coulomb constant, k

9×10⁹

Electric field

regions around an electrically charged particle or object within which a force would be exerted on other electrically charged particles or objects

Electric field strength, E

the intensity of an electric field at a particular location

Electric field lines

Imaginary lines showing the direction of the force that would act on a positive test charge

Point charge

An idealised charged object whose dimensions are negligible compared with the distances involved

Electric potential difference / voltage

the change in potential energy per unit charge between two defined points in a circuit

Equipotential

A line or surface on which every point has the same electric potential. No work is required to move a charge along an equipotential

Magnetic field

a region of space near a magnet, electric current or moving electrically charged particle in which a magnetic force acts on any other magnet, electric current or moving electrically charged particle

Magnetic field strength / magnetic flux density, B

the strength of a magnetic field or the number of magnetic field lines per unit area

Magnetic field lines

Lines representing the direction and relative strength of a magnetic field. Outside a magnet they point from north to south

Conventional current

The defined direction of current corresponding to the movement of positive charge, opposite to electron flow in metals

Fleming’s Left Hand Rule

Direction of force/motion on a current-carrying conductor in a magnetic field — the motor effect

Thumb = Force

First Finger = Field (N to S)

Second Finger = Conventional Current

Fleming’s Right Hand Rule

Direction of induced conventional current when a conductor moves through a magnetic field — the generator effect/electromagnetic induction

Thumb = Motion (Force)

First Finger = Field (N to S)

Second Finger = Induced Current

Right Hand Grip Rule

A rule used to determine the direction of the magnetic field around a current-carrying conductor. Point your right thumb in the direction of conventional current, and your curled fingers show the direction of the magnetic field lines

Magnetic flux, Φ

a measurement of the total magnetic field that passes through a given area; a measure of the number of magnetic field lines passing through the given area

Electromagnetic induction

The production of an EMF due to a change in magnetic flux through a conductor or circuit

Faraday's Law

a law stating that when the magnetic flux linking a circuit changes, an electromotive force is induced in the circuit proportional to the rate of change of the flux linkage

Lenz's Law

states that the direction of an induced electric current always opposes the change in the circuit or the magnetic field that produces it

Generator

A device that converts mechanical energy into electrical energy using electromagnetic induction

Alternating current (AC)

Electric current that periodically reverses direction

Electromagnetic wave

produced by an oscillating electric charge resulting in mutually perpendicular electric and magnetic fields

Frame of reference

A coordinate system relative to which the position and motion of objects are measured

Inertial frame of reference

any frame of reference with respect to which the acceleration of the object of observation remains zero

Principle of relativity

The laws of physics are the same in all inertial frames of reference

Special theory of relativity

Einstein's theory describing space and time for observers in inertial frames, based on the principle of relativity and invariance of the speed of light

Speed of light postulate

The speed of light in a vacuum has the same value ccc for all inertial observers, regardless of the motion of the source or observer

Event

Something that occurs at a specific position and time in spacetime

Observer

A person or reference frame from which measurements of events, positions and times are made

Simultaneity

the relation between two events assumed to happen at the same time in a frame of reference

Relativity of simultaneity

Events simultaneous in one inertial frame may not be simultaneous in another frame moving relative to the first

Proper time

the time interval measured in the frame of reference in which the object is at rest. It is the shortest measured time interval.

Time dilation

the difference of elapsed time between two events as measured by observers moving relative to each other

Proper length

The length of an object measured in the reference frame in which the object is at rest. It is the maximum measured length.

Length contraction

an observer at rest relative to a moving object would observe the moving object to be shorter along the dimension of motion, and the observer in the moving object would observe a contracted distance between places in space

Rest mass

The mass of an object when measured in the same reference frame as the observer

Mass–energy equivalence

The principle that mass and energy are equivalent and interchangeable, expressed by E=mc²

Relativistic momentum

the momentum of an object when measured in the frame of reference in which the object is in motion

Lorentz factor, γ

A factor describing relativistic effects, 1/root (1-(v²/c²))

Relativistic energy

Energy of an object accounting for relativistic effects.

Classical limit

At speeds much smaller than ccc, relativistic equations approximate classical Newtonian results because γ≈1

Black body

An ideal object that absorbs all incident electromagnetic radiation and is also a perfect emitter of thermal radiation

Black-body radiation

Electromagnetic radiation emitted by an ideal black body due to its temperature

Black-body spectrum

The distribution of radiation intensity emitted by a black body across different wavelengths

Wien's displacement law

The wavelength of maximum emission is inversely proportional to absolute temperature

Ultraviolet catastrophe

The incorrect classical prediction that a black body should emit unlimited energy at short wavelengths

Quantisation

The principle that certain physical quantities, such as energy, can exist only in discrete values rather than continuously

Quantum

A discrete packet or smallest allowed amount of a physical quantity such as electromagnetic energy

Planck's hypothesis

Energy is emitted or absorbed in discrete packets with energy proportional to frequency

Wien’s displacement constant, b

2.898×10^-3

Planck’s constant, h

6.626×10^-34

Photoelectric effect

The emission of electrons from a material when electromagnetic radiation of sufficiently high frequency is incident upon it

Photoelectron

An electron emitted from a material as a result of the photoelectric effect

Work function, ϕ

the minimum energy required to remove an electron from a solid

Threshold frequency, f₀

the minimum frequency of a photon that can eject an electron from a surface

Threshold wavelength

The maximum wavelength of incident radiation capable of causing photoelectron emission

Stopping potential

The minimum reverse potential difference required to stop the most energetic photoelectrons from reaching the collector

Rutherford model

An atomic model in which most mass and positive charge are concentrated in a tiny nucleus, with electrons surrounding it and mostly empty space between

Limitations of Rutherford model

• Could not explain atomic stability — according to classical physics, accelerating/orbiting electrons should continuously emit energy, lose energy and eventually spiral into the nucleus.

• Could not explain discrete atomic emission and absorption spectra, such as the hydrogen line spectrum.

• Did not include quantised electron energy levels.

Bohr model

An atomic model in which electrons occupy discrete, quantised energy states around the nucleus and emit or absorb photons when transitioning between states

Limitations of Bohr model

• Works well primarily for hydrogen and hydrogen-like atoms with only one electron.

• Does not accurately explain the spectra of multi-electron atoms.

• Treats electrons as travelling in fixed circular orbits, which is inconsistent with the modern quantum-mechanical description of electrons as having probabilistic distributions/orbitals.

• Cannot fully explain finer details in atomic spectra.

Ground state

The lowest possible energy state of an atom or electron

Excited state

Any allowed energy state above the ground state

Emission spectrum

A spectrum of discrete wavelengths emitted when electrons transition from higher to lower energy states

Absorption spectrum

A spectrum containing missing wavelengths produced when atoms absorb photons that cause electrons to transition to higher energy states

Rydberg equation

An equation used to calculate wavelengths associated with electron transitions in hydrogen

Rydberg constant, R

1.097×10⁷

Wave–particle duality

The principle that quantum objects such as light and matter can display both wave-like and particle-like properties depending on how they are observed

Wave model of light

uses the characteristics of waves such as wavelength, frequency and speed to describe the behaviour of light such as interference and refraction

Particle model of light

A model describing light as discrete photons, explaining phenomena such as the photoelectric effect

de Broglie wavelength

The wavelength associated with a particle's momentum

Diffraction

a phenomenon in which waves either bend behind a barrier or the wavefront is broken up into many small sources

Interference

The combination of waves through superposition, producing constructive and destructive patterns; evidence of wave behaviour

Standard Model

The theory describing fundamental particles and three fundamental interactions: electromagnetic, strong and weak interactions

Elementary particle

a particle whose substructure is unknown

Fermion

A fundamental matter particle

Quark

subatomic particles governed by the strong nuclear force that constitute hadrons

Antiquark

The antiparticle of a quark, with opposite quantum properties

Hadron

A composite particle made of quarks and held together by the strong interaction

Baryon

A hadron composed of three quarks. Examples include protons and neutrons

Meson

A hadron composed of a quark and an antiquark

Lepton

particles that are governed by the weak nuclear force and, since they have charge, are also influenced by electromagnetism (not neutrinos tho)

Gauge boson

carrier or exchange particles that govern particle interaction and the mediation of the fundamental forces

Six Quarks

First Gen: Up, Down

Second Gen: Charm, Strange

Third Gen: Top, Bottom

(+2/3e, -1/3e)

Six Leptons

First Gen: Electron, Electron neutrino

Second Gen: Muon, Muon neutrino

Third Gen: Tau, Tau neutrino

(-1e, 0e)

First, Second, Third Generations

First gen is lightest and most stable, third gen is heaviest and most unstable

Antiparticle

a particle with the same mass and opposite charge and/or spin to a corresponding particle, for example positron and electron