Paper 1 definitions (A-Level Physics)

Acceleration

change of velocity per unit time

acceleration of free fall

accelerated object by gravity

Accurate

correctly calibrated instruments

Accuracy

closeness to real value

Alpha radiation

2 protons and 2 neutrons

Amplitude

maximum displacement of a vibrating particle from equilibrium

Annihilation

Particle and antiparticle meet, destroy eachother and emit radiation

Anti-baryon

Hardon with 3 antiquarks

Antinode

Fixed point on stationary wave where amplitude is maximum

Antiparticle

Antiparticle for every particle. Equal rest mass, opposite charge

Atomic Number, Z

Number of protons

Baryon

Hadron with 3 quarks

Base units

Units that define the SI system (e.g., the metre, the kilogram, the second, the ampere)

Beta radiation

Beta (-) particles are fast moving electrons emitted by unstable neutron-rich nuclei or when free neutrons decay.

Beta (+) particles are fast moving positrons emitted by unstable proton-rich nuclei.

Braking distance

distance travelled in time taken for vehicle to stop

Brittle

Snaps without stretching or bending when subject to stress

Centre of mass

The point through which a single force on the body has no turning effect

Charge carriers

Charged particles that move through a substance when a pd is applied across it.

Circuit rule for current (Kirchhoff's first law)

1. Current passing through 2 or more components in series is the same through each component.

2. At junction, total current in = total current out

Circuit rule for pd (Kirchhoff's second law)

1. For 2 or more components in series, total pd across all components is equal to sum of pd's across each component.

2. Sum of emfs around a complete loop in a circuit= sum of pd's around the loop

Coherent

2 sources of waves that have a constant phase difference

Conservation rules

For particle interactions these must be conserved:

energy, momentum, charge , baryon number, lepton number.

Strangeness is only conserved in strong interactions.

Couple

pair of equal and opposite forces acting on a body but not acting along the same line of action

Critical angle

incidence > critcal for TIR

(angle of incidence for a light ray must exceed critical angle for total internal reflection to occur)

Critical temperature of superconducting material

Temperature at and below where resistivity is zero

Cycle

interval for a vibrating particle (or wave) from a certain displacement and velocity to the next time that it has the same displacement and velocity

De Broglie hypothesis

particles have wave-like nature

De broglie wavelength

Wavelength of a matter material (=h/p, p is the momentum of the particle)

De-excitation

Atom loses energy by photon emission as a result of an electron moving down an energy level.

Density of substance

Mass per unit volume of the substance

Diffraction

spreading of waves after passing through a gap (or near an edge)

Diffraction grating

a plate with many closely-ruled parallel slits on it

Dispersion

splitting a beam of white light into colours through a glass prism

Displacement

distance and direction from equilibrium position

Drag force

the force of fluid resistance on an object moving through the fluid

Ductile

stretches easily without breaking

Efficiency

useful output / total input (by a machine or device)

Effort

force applied to make a machine move

Elastic limit

Point beyond which a wire is permanently stretched

Elasticity

property of a solid that enables it to return to its original shape after being deformed (or distorted)

Electrolysis

Process of electrical conduction in a solution (or molten compound) due to ions moving to the oppositely charged electrode

Electrolyte

a solution (or molten compound) that conducts electricity

Electromagnetic force

force between two charged objects

Electromagnetic wave

a photon (or wave packet) consisting of transverse electric and magnetic waves in phase and at right angle to each other

Electromotive force (emf)

the amount of electrical energy per unit charge produced inside a source of electrical energy

Electron capture

Process where an inner-shell electron of an atom is captured by the nucleus

Electron volt

the work done when an electron is move through a p.d. of 1V (=1.6x10^-19)

Endoscope

Optical fibre device used to see inside cavities

Energy

the capacity to do work

Energy levels

the energy of an electron in an electron shell of an atom

Equilibrium

state of an object when at rest or in uniform motion (zero acceleration)

Error bar

A representation of uncertainty on a graph

Error of measurement

Uncertainty of a measurement. Errors include systematic (zero error) and random.

Excitation

process where an atom absorbs energy (a photon) causing an electron to go up an energy level

First harmonic

Pattern formed by a stationary wave when the string vibrates at its lowest possible frequency.

Fluorescence

Light emitted from a substance exposed to UV radiation. Atom de-excite in stages and emit visible photon in process.

Force

Any interaction that can change the velocity of an object

Free body diagram

A diagram representing all forces acting on an object

Frequency

number of oscillations per second

Friction

The resistive force that opposes the motion or attempted motion of an object either past another object with which it is in contact or through a fluid.

Gamma radiation

high energy photons emitted by unstable nuclei or produced in particle annihilations

Gravitational field strength

force of gravity per unit mass on a small object

Ground state

lowest energy state of an atom

Hadron

Particles and antiparticles that can interact via the strong interaction

Hooke's Law

Extension of a spring is directly proportional to the force applied provided the limit of proportionality is not exceeded.

Inertia

Resistance of an object to change of its motion

Interference

formation of points of cancellation and reinforcement when two coherent waves pass through each other

Internal resistance

the loss of pd per unit current in the source when current passes through it. (resistance inside a source of electrical energy)

Ion

A charged atom

Ionisation

process of creating ions

Isotopes

Different number of neutrons. Same number of protons.

Kaon (K meson)

a meson that consists of a strange quark or antiquark and another quark or antiquark

Kinetic energy

the energy of an object due to its motion (KE=1/2mv^2)

Laser

device that produces a parallel coherent beam of monochromatic light

Lepton

Cannot interact through the strong interaction. All interact via weak interaction. Charged leptons also interact via electromagnetic interaction.

(Electrons, positrons, muons, anitmuons, neutrinos and their antiparticles. )

Lepton number

Leptons are (+1) and anti-leptons are ( -1). Total lepton number in an interaction is always conserved.

Light-dependent resistor

A component that decreases resistance as light intensity increases.

Limit of proportionality

The limit beyond which, when a wire or spring is stretched, the extension is no longer directly proportional to the force applied.

Load

the force overcome by a machine to raise (or shift) an object

Longitudinal waves

the oscillation of particles is parallel to the direction of the wave (e.g sound)

Mass

the measure of inertia

Matter waves

The wave-like behaviour of particles of matter

Meson

A hadron consisting of a quark and an antiquark

Modal dispersion

the lengthening of a light pulse as it travels along an optical fibre, due to rays that repeatedly undergo total internal reflection having to travel a longer distance than rays that undergo fewer total internal reflections

Moment of a force about a point

Force x perpendicular distance from the line of action of the force to the point

Momentum

mass x velocity

Motive force

the force that drives a vehicle

Muon

a lepton which is negatively charged and has a greater rest mass then the electron

Negative temperature coefficient

Resistance of a semiconductor decreases when the temperature in increased

Neutrino

Uncharged lepton with very small rest mass compared with electron

Neutrino types

3 types. Electron neutrino, muon neutrino and tau neutrino.

Newton's First law

an object remains at rest or in uniform motion unless acted on by a resultant force.

Newton's Second law

the rate of change of momentum of an object is proportional to the resultant force acting on it.

(F=Δmv/Δt). (Constant mass , F=ma)

Newton's Third law

For every action there is an equal and opposite reaction of the same type.

Node

Fixed point on a stationary wave where the amplitude is zero.

Nucleon

A neutron or proton in the nucleus

Nucleon number (A)

the number of neutrons and protons in a nucleus

(also called mass number)

Nuclide

a type of nucleus with a specific number of protons and neutrons.

Ohm's Law

the pd across a metallic conductor is proportional to the current, provided no physical conditions change.

Optical fibre

a thin flexible transparent fibre used to carry light pulses from end to the other