AS/2 OCR Physics- The Motherload.
Doppler equation
(∆λ)/λ ≈ (∆f)/f ≈ v/c Where 'λ' is the source wavelength, '∆λ' is the change in wavelength recorded by the observer, 'f' is the source frequency, '∆f' is the change in frequency recorded by the observer, 'v' is the magnitude of the relative velocity between the source and the observer, and 'c' is the speed of light through a vacuum (3.00x10⁸ms⁻¹)
Electronvolt
A derived unit of energy used for subatomic particles and photons, defined as the energy transferred to or from an electron when it passes through a potential difference of 1 volt; 1 eV is equivalent to 1.60x10⁻¹⁹J
Kilowatt-hour
A derived unit of energy, most often associated with paying for electrical energy, symbol kWh (1kWh=3.6MJ). Energy in kWh can be calculated by multiplying the power kW by the time in hours
I-V characteristic
A description of the relationship between the electric current in a component and the potential difference across it -- in most cases this is usually in the form of a simple graph of I against V
Cloud chamber
A detector of ionising radiation consisting of a chamber filled with air saturated with vapour at a very low temperature so that droplets of liquid condense around ionised particles left along the path of radiation
Electricity meter
A device that measures the electrical energy supplied in kWh to a house from the grid
Cell
A device that transfers chemical energy into electrical energy
Electron gun
A device that uses a large accelerating potential difference to produce a narrow beam of electrons
Velocity selector
A device that uses both electric and magnetic fields to select charged particles of specific velocity
Ultrasound transducer
A device used both to generate and to receive ultrasound, which changes electrical energy into sound and sound into electrical energy
Ammeter
A device used to measure electric current-- it must be placed in series and ideally have zero resistance
Voltmeter
A device used to measure potential difference -- it must be placed in parallel across the components and ideally have an infinite resistance
Gold-leaf electroscope
A device with a metallic stem and a gold leaf that can be used to identify and measure electric charge -- a device that was historically used as a voltmeter for measuring large voltages
Free-body diagram
A diagram that represents the forces acting on a single object
Eneru level
A discrete (quantised) amount of energy that an electron within an atom is permitted to possess
Optical fibre
A fibre made of glass designed with a varying refractive index in order to totally internally reflect pulses of visible or infrared light travelling through it
Gravitational field
A field created around any object with mass, extending all the way to infinity, but diminishing as the distance from the centre of mass of the object increases
Centripetal force
A force that keeps a body moving with a constant speed in a circular path
Restoring force
A force that tries to return a system to its equilibrium position
Loading curve
A force-extension graph
Lepton
A fundamental particle or antiparticle that is not affected by the strong nuclear force -- for example, an electron
Elementary perticle
A fundemental particle
Coupling gel
A gel with acoustic impedance similar to that of skin smeared onto the transducer and the patient's skin before an ulstrasound scan in order to fill air gaps and ensure that almost all the ultrasound enters the patients body
Diffraction grating
A glass or plastic slide on which as many as 1000 lines in a millimetre are ruled, at a spacing that diffracts visible wavelengths of light
Force-extension graph
A graph of force against extension (or compression), with the area under the graph equal to the work done on the material
Force-time graph
A graph of net force against time, with the area under the graph equal to the impulse
Wave profile
A graph showing the displacement of the particles in the wave against the distance along the wave
Hertzsprung-Russell diagram
A graph showing the relationship between the luminosity of stars in out galaxy (on the y axis) and their average surface temperature (on the x axis, with the temperature increasing from right to left)
Uniform gravitational field
A gravitational field in which field lines are parallel and the value for g remains constant
Red supergiant
A huge star in the last stages of its life before it 'explodes' in a supernova
Dark energy
A hypothetical form of energy that fills all of space and would explain the accelerating expansion of the Universe
Dark matter
A hypothetical form of matter spread throughout the galaxy that neither emits or absorbs light- it could explain the differences between the predicted and observed velocities of stars in galaxies
Neutrino
A lepton (a fundamental particle) that carries no charge and may have tiny mass, less than a millionth the mass of an electron
Spectral line
A line in an emission line spectrum or absorption line spectrum at a specific wavelength
Wavefront
A line of points in phase with each other in a wave, perpendicular to the direction of energy transfer
Isotherm
A line on a pressure-volume graph that connects points at the same temperature
Ray
A line representing the direction of energy transfer of a wave, perpendicular to the wavefronts
Kepler's second law of planetary motion
A line segment connecting a planet to the Sun sweeps out equal areas during equal intervals of time
Electrolyte
A liquid containing ions that are free to move and so to conduct electricity
Hysteresis loop
A loop-shaped plot obtained when, for example, loading and unloading a material produce different deformations
Fiducial marker
A marker for a point used as a fixed basis for measurement or comparison
Point mass
A mass with negligible volume
Strong material
A material with a large value for the ultimate tensile strength
Semiconductor
A material with a lower number density than a typical conductor, for example silicon
Attenuation coefficient
A measure of absorption of X-ray photons by a substance, also known as absorption coefficient- SI unit m⁻¹
Absorption coefficient
A measure of the absorption of X-ray photons by a substance, also known as attenuation coefficient- SI uni m⁻¹
Amount of substance
A measure of the amount of matter in moles
Eccentricity
A measure of the elongation of an ellipse
Target metal
A metal with high melting point used for the anode in an X-ray tube, for example tungsten
Carbon dating
A method for determining the age of organic material, by comparing the activities, or the ratios, of carbon-14 to carbon-12 nuclei of the dead material of interest and similar living material
Crystallography
A method for determining the structure of a substance by studying the interference patterns produced by the waves passing through a crystal of the substance
Arcminute
A minute of arc; 1°=60 arcminutes
Fleming's left hand rule
A mnemonic for the direction of force experienced by a current-carrying wire placed perpendicular to the external magnetic field: on the left hand, the first finger gives the direction of the external magnetic field, the second finger gives the direction of current, and the thumb gives the direction of motion (force) of the wire
Ideal gas
A model of gas including assumptions that simplify the behaviour of real gases
Kinetic model
A model that describes all substances as made of atoms, ions or molecules, arranged differently depending on the phase of the substance
Conventional current
A model used to describe electric current in a circuit -- conventional current travels from positive to negative -- it is the direction in which positive charges would travel
Compression (waves)
A moving region in which the medium is denser or has a higher pressure than the surrounding medium
Rarefaction (waves)
A moving region in which the medium is less dense or has less pressure than the surrounding medium
Cathode
A negatively charged electrode
Anion
A negatively charged particle, one which is attracted to an anode
Beta decay
A neutron in an unstable nucleus decays into a proton, an electron or an antineutrino (β⁻ decay), or a proton into a neutron, a positron and an electron neutrino (β⁺ decay)
Thermal neutron
A neutron is a fission reactor with mean kinetic energy similar to the thermal energy of particles in the reactor core - also known as a slow neutron
Daughter nucleus
A new nucleus formed following a radioactive decay
Parent nucleus
A nucleus before the occurrence of radioactive decay
Couple
A pair of equal and opposite forces acting on a body but not in the same straight line
Nucleon
A particle in the nucleus of an atom, either a proton or a neutron
Hadron
A particle or antiparticle that is affected by the strong nuclear force, and, if charged, by the electromagnetic force - for example, a proton
Fundamental particle
A particle that has no internal structure and hence cannot be split into smaller particles
Charge carrier
A particle with a charge that moves through a material to form an electric current- e.g., an electron in a metal wire
Interference pattern
A pattern of consecutive and destructive interference formed as waves overlap
Inflation
A phase of astonishing acceleration of the expansion of the Universe thought to have occurred 10⁻³⁵s after the Big Bang
Phase
A phase of matter is its state (solid, liquid, or gas)
Superconductivity
A phenomenon in which the resistivity of a material falls to almost zero when the material is cooled below a certain temperature
Electric charge
A physical property, symbol 'q' or 'Q', either positive or negative, measured in coulombs 'C' or as a relative charge
X-ray tube
A piece of equipment that produces X-ray photons by firing electrons from a heated cathode across a large p.d. in an evacuated tube - X-ray photons are produced when the electrons are decelerated by hitting the target metal of the anode
Solar system
A planetary system consisting of a star and at least one planet in orbit around it - our own Solar System contains the Sun and all objects that orbit it
Pivot
A point at which a body can rotate
Yield point
A point on a stress-strain graph beyond which the deformation is no longer entirely elastic
Centre of mass
A point through which any externally applied force produces straight-line motion but no rotation
Negative temperature coefficient (NTC)
A relationship in which a variable decreases as the temperature increases, for example the resistance of NTC thermistors
Elastic deformation
A reversible change in the shape of an object due to a compressive or tensile force -- removal of stress or force will return the object to its original shape and size (no permanent strain)
Geostationary satellite
A satellite that remains in the same position relative to a spot on the Earth's surface, by orbiting in the direction of the Earth's rotation over the equation with a period of 24 hours
Absolute scale of temperature
A scale for measuring temperature based on absolute zero and the triple point of pure water, with the gradations equal in size to those of the Celsius scale;unit kelvin (K)
Thermodynamic scale of temperature
A scale for measuring the temperature based on absolute zero and the triple point of pure water, with gradations equal in size to those of the Celsius scale; unit kelvin (K)
Arcsecond
A second of arc; 1 arcminute = 60 arcseconds
Diode
A semiconductor component that allows current only in one particular direction
Emission line spectrum
A set of specific frequencies of electromagnetic radiation, visible as bright lines in spectroscopy, emitted by excited atoms as their electrons make transitions between higher and lower energy states, losing the corresponding amount of energy in the form of photons as they do so - every element has a characteristic line spectrum
Absorption line spectrum
A set of specific frequencies of electromagnetic radiation, visible as dark lines in an otherwise continuous spectrum on spectroscopy. They are absorbed by atoms as their electrons are excited between energy states by absorbing the corresponding amount of energy in the form of photons- every element has a characteristics line spectrum
Conical pendulum
A simple pendulum that, instead of swinging back and forth, rotates in a horizontal circle at a constant speed
Relative charge
A simplified measurement of the electric charge of a particle or object, measures as multiples of the elementary charge
Resultant vector
A single vector that has the same effect as two or more vectors added together
Comet
A small, irregular body made of ice, dust, and small pieces of rock in an (often highly eccentric elliptical) orbit around the Sun - as they approach the Sun, some comets develop spectacular tails
Wave source
A source of waves, such as light or sound - the object moving relative to an observer of the Doppler effect
Continuous spectrum
A spectrum in which all visible frequencies or wavelengths are present (a heated solid metal such as lamp filament will produce this type of spectrum)
Velocity
A vector quantity equal to the rate of change of displacement
White dwarf
A very dense star formed from the core of a red giant, in which no fusion occurs
Protostar
A very hot, very dense sphere of condensing dust and gas that is on the way to becoming a star
Fundamental mode of vibration
A vibration at the fundamental frequency
Longitudinal wave
A wave in which the medium is displaced in the same line as the direction of energy transfer -- oscillations of the medium particles are parallel to the direction of the wave travel
Transverse wave
A wave in which the medium is displaced perpendicular to the direction of energy transfer - the oscillations of medium particles are perpendicular to the direction of travel of the wave
Progressive wave
A wave in which the peaks and troughs, or compressions and rarefactions, move through the medium as energy is transferred
Standing / stationary wave
A wave that remains in a constant position with no net transfer of energy and is characterised by its nodes and antinodes
Harmonic
A whole-number multiple of the fundamental frequency
Prefix
A word or letter placed before another one, for example 5.0km is 5.0x10³m
Kinetic theory of matter
All substances are made of atoms, ions or molecules, arranged differently depending on the phase of substance
Mass
Amount of matter, a base quantity measured in kilograms, kg
Black body
An idealised object that absorbs all the electromagnetic radiation incident on it and, when in thermal equilibrium, emits a characteristic distribution of wavelengths at a specific temperature.
Normal
An imaginary line perpendicular to a surface such as the boundary between one medium and another (e.g. air and glass)
Centre of gravity
An imaginary point at which the entire weight of an object appears to act
Oscilloscope
An instrument that displays an electrical signal as a voltage against time trace on a screen
Ionic solution
An ionic compound dissolved in a liquid to form an electrolyte
Plastic deformation
An irreversible change in the shape of an object due to a compressive or tensile force -- removal of the stress of the force produces permanent deformation
Closed system
An isolated system that has no interaction with its surroundings
Planet
An object in orbit around a star with a mass large enough for its own gravity to give it a round shape, that undergoes no fusion reactions, and that has cleared its orbit of most other objects
Projectile
An object that is thrown or propelled on the surface of the Earth
Damping
An oscillation i damped when an external force that acts on the oscillator has the effect of reducing the amplitude of its oscillations
Forced oscillation
An oscillation in which a periodic driver force is applied to an oscillator
Isochronous oscillator
An oscillator that has the same period regardless of amplitude
c
Centi,10⁻²
Loading (electrical circuits)
Connecting a component or a device across the terminals of a source of e.m.f. or across another component
Heavy damping
Damping that occurs when the damping forces are large and the period of the oscillations increases slightly with the rapid decrease in amplitude
Light damping
Damping that occurs when the damping forces are small and the period of the oscillations is almost unchanged
d
Deci, 10⁻¹
Electromotive force (e.m.f)
Defined as the energy transferred from chemical to electric energy per unit charge
Potential difference (p.d.)
Defined as the energy transferred from electrical energy to other forms (heat, light, etc.) per unit charge
Polymeric
Description of a material comprising of long-chain molecules, such as rubber, which may show large strains
Plane polarised
Description of a transverse wave in which the oscillations are limited to only one plane
Unpolarised
Description of a transverse wave in which the oscillations occur in many places
Partially polarised
Description of a transverse wave in which there are more oscillations in one particular plane, but the wave is not completely plane polarised-- occurs when transverse waves reflect off a surface
Breaking distance
Distance travelled by a vehicle from the time the brakes are applied until the vehicle stops
Photoelectric effect equation
Einstein's equation relating the energy of a photon, the work function of a metal, and the maximum kinetic energy of any emitted photoelectrons: hf=φ+KE(max)
Infrared waves
Electromagnetic waves, with wavelengths from 10⁻³m to 7x10⁻⁷m
Ultraviolet
Electromagnetic waves, with wavelengths from 4x10⁻⁷m to 10⁻⁸m
Visible light
Electromagnetic waves, with wavelengths from 4x10⁻⁷m to 7x10⁻⁷m
Photoelectrons
Electrons emitted from the surface of metal by the photoelectric effect
Principle of moments
For a body in rotational equilibrium, the sum of the anticlockwise moments about a point is equal to the sum of the clockwise moments about the same point
Right-hand grip rule
For a current-carrying wire, the thumb points in the direction of the conventional current, and the direction of the field is given by the direction in which the fingers of the right hand would curl around the wire
Triple point
For a given substance, one specific of that substance can exist in thermodynamic equilibrium
Node
For a stationary wave, a point where the amplitude is always zero
G
Giga, 10⁹
Gas pressure
In stars, the pressure of the nuclei in the star's core pushing outwards and counteracting the gravitational force pulling the matter in the star inwards
Parallel (vectors)
In the same line and direction
Antiparallel (vectors)
In the same line but opposite directions
Beta radiation
Ionising radiation consisting of fast-moving electrons (β⁻) or (β⁺) emitted from unstable nuclei, with a charge of -e or +e respectively
Gamma radiation
Ionising radiation consisting of high-energy photons, with wavelengths less than about 10⁻¹³m, which travel at the speed of light
Alpha radiation
Ionising radiation consisting of particles comprising two protons and two neutrons (a helium nucleus), with a charge of +2e
Microwaves
Long-wavelength electromagnetic waves, with wavelengths from 10⁻¹m to 10⁻³m
Radio waves
Long-wavelength electromagnetic waves, with wavelengths greater than 10⁻¹m
Standard form
Mathematical notation in which a number is shown with the decimal point is placed after the first digit, followed by x10 raised to the appropriate power
M
Mega, 10⁶
μ
Micro, 10⁻⁶
m
Milli, 10⁻³
n
Nano, 10⁻⁹
Induced fission
Nuclear fission occurring when a nucleus becomes unstable on absorbing another particle (such as a neutron)
Isotopes
Nuclei of the same element that have the same atomic numbers (number of protons) but different nucleon numbers (numbers of neutrons)
k
Kilo, 10³
Atomic mass unit
One atomic mass unit (1u) is one-twelfth the mass of a neutral carbon-12 atom.
Strong nuclear force
One of four fundamental forces in nature, acting on hadrons and holding nuclei together
Weak nuclear force
One of four fundamental forces in nature, responsible for inducing beta-decay within unstable nuclei
Base unit
One of seven units that form the building blocks of the SI system
Component
One of the two perpendicular vectors obtained by resolving a vector
Positive (charge)
One type of electric charge -- positively charged objects attract negatively charges ones, and repel other positive charges
Negative (charge)
One type of electric charge; negatively charged objects attract positively charged ones, and repel other negative charges
Simple harmonic motion
Oscillating motion for which the acceleration of the object is directly proportional to its displacement and is directed towards some fixed point - characterised by the equation a=ω²x
Superposition (waves)
Overlap of two waves at a point in space
P
Peta, 10¹⁵
P-waves
Primary waves- longitudinal waves that travel through the Earth from an earthquake
Control rods
Rods made of a material whose nuclei readily absorb neutrons (commonly boron or cadmium), which can be moved to ensure that exactly one slow neutron survives per fission reaction or to completely stop the fission raction
S-waves
Secondary waves: transverse waves that travel through the Earth from an earthquake
X-rays
Short wavelength electromagnetic waves, with wavelengths from 10⁻⁸m to 10⁻¹³m, which can be used in medical imaging
Gamma rays
Short-wavelength electromagnetic waves, with wavelengths from 10⁻¹⁰m to 10⁻¹⁶m
Resolving a vector
Splitting a vector into two component vectors perpendicular to each other
Kelvin
The SI base unit of the absolute (thermodynamic) scale of temperature
Stiffnes
The ability of an object to resist deformation
Centripetal acceleration
The acceleration of any object travelling in a circular path at constant speed, which always acts towards the centre of the circle
Mole
The amount of substance that contains as many elementary entities as there are atoms in 0.012kg (12g) of carbon-12
Angle of reflection
The angle between the direction of travel of a reflected wave ant the normal at a boundary between two medias
Angle of incidence
The angle between the direction of travel of an incident wave and the normal at a boundary between two media.
Critical angle
The angle of incidence at the boundary between two media that will produce an angle of refraction of 90°
Law of reflection
The angle of incidence is equal to the angle of reflection
Parallax angle
The angle of the apparent shift in the position of a relatively close star against the backdrop of much far more distant stars as the Earth makes a quarter an orbit around the Sun
Radian
The angle substituted by a circular arc with a length equal to the radius of a circle (approximately 57.3°)
Antiparticle
The antimatter counterpart of a particle, with the opposite charge to the particle (if the particle has charge) and exactly the same rest mass as the particle
Positron
The antiparticle of the electron
Impulse
The area under a force-time graph -- the product of force and the time for which the force acts
Cosmological principle
The assumption that, when viewed on a large enough scale, the Universe is homogeneous and isotropic, and the laws of physics are universal
Proton number
The atomic number, that is, the number of protons in a nucleus- symbol Z
Quantisation
The availability of some quantities, such as energy or charge, only in certain discrete values
Half-life
The average time it takes for half the number of active nuclei in a sample of an isotope to decay
Mean drift velocity
The average velocity of electrons as they move through a wire, symbol 'v', unit ms⁻¹
Ampère
The base SI unit of electric current, symbol A, defined as the current flowing in two parallel wires in a vacuum 1m apart such that there is a n attractive force of 2.0 x 10⁻⁷ N per metre length of wire between them
Binding energy per nucleon
The binding energy divided by the number of protons and neutrons in the nucleus; the greater the binding energy per nucleon, the more tightly bound are the nucleons within the nucleus
Quantum mechanics
The branch of physics dealing with phenomena on the very small scale, often less than the size of an atom
Gravitational potential energy
The capacity for doing work as a result of an object's position in a gravitational field
Energy
The capacity for doing work, measured in joules, J
Refraction
The change in direction of a wave as it changes speed when it passes from one medium to another
Reflection
The change in the direction of a wave at a boundary between two media, so that the wave remains in the original medium
Average velocity
The change in the displacement ∆t; ∆s / ∆t
Doppler effect
The change in the frequency and wavelength of waves received from an object moving relative to an observer compared with what would be observed without relative motion
Capacitance
The charge stored per unit of potential difference across a capasitor
Perihelion
The closest point to the Sun in an orbit
Annihilation
The complete destruction of a particle and its antiparticle in an interaction that releases energy in the form of identical photons
Gravitational constant, G
The constant in Newton's law of gravitation F=(GMm)/r², with a value determined from the experiment of 6.67x10⁻¹¹Nkg⁻²m²
Molar gas constant
The constant in the equation of the state of an ideal gas- symbol 'R', 8.31J⁻¹mol⁻¹
Terminal velocity
The constant speed reached by an object when the drag force (and upthrust) is equal to the weight of the object
Stephan constant
The constant σ in Stephan's law, : L=4πr²σT⁴, relating the luminosity, L, of a star to its surface area, 4πr², and its absolute surface temperature T: σ=5.67x10⁻⁸Wm⁻²K⁻⁴
Brownian motion
The continuous random motion of small particles suspended in a fluid, visible under a microscope
Standard model
The current theory of particle physics that deals with elementary particles (quarks, electrons, etc.) and their interactions
Compression
The decrease in length of an object when a compressive force is exerted on it
Attenuation
The decrease in the intensity of electromagnetic radiation as it passes through matter and/or space
Coulomb
The derived SI unit of electrical charge, symbol C; 1 coulomb of electrical charge passes a point in 1 second when there is an electrical current of 1 ampère, 1C=1As
Volt
The derived SI unit of potential difference and electromotive force, symbol V, defined as the energy transferred to or from the charges - 1V is the p.d. across the component when 1J of energy is transferred over 1C passing through the component
Ohm
The derived SI unit of resistance, symbol Ω -- defined as the resistance of a component that has a potential difference of 1V per unit ampere
Phase difference
The difference between the displacements of particles along a wave, or the difference between the displacements of particles on different waves, measured in degrees or radians, with each complete cycle or difference of one wavelength representing 360° or 2π radians
Mass defect
The difference between the mass of a nucleus and the mass of its completely separated constituent nucleons
Phase difference (for oscillating motion)
The difference in displacement between two oscillating objects or the displacement of an oscillating object at different times - symbol φ
Path difference
The difference in the distance travelled by two waves from their source to a specific point
Lenz's law
The direction of the induced e.m.f or current is always such as to oppose the change producing it
Parsec
The distance at which a radius of one AU subtends an angle of one arcsecond
Displacement (waves)
The distance from the equilibrium position in a particular direction -- displacement is a vector, so it has a positive or negative value`
Thinking distance
The distance travelled by a vehicle from when the driver first perceives a need to stop to when the breaks are applied
Light-year
The distance travelled by light in a vacuum in a time of one year (9.46x10¹⁵m)
Wave speed
The distance travelled by the wave per unit time
Displacement
The distance travelled in a particular direction -- it is a vector with magnitude and direction
Maxwell-Boltzmann distribution
The distribution of the speeds of particles in a gas
Air resistance
The drag or resistive force experienced by objects moving through air.
Elementary charge
The electric charge equivalent to the charge of a proton, 1.60x10⁻¹⁹C; symbol 'e'
Thermionic emission
The emission of electrons from the surface of a hot metal wire
Photoelectric effect
The emission of photoelectrons from a metal surface when electromagnetic radiation above a threshold frequency is incident on the metal
Kinetic energy
The energy associated with an object as a result of its motion
Ground state
The energy level with the most negative value possible for an electron within an atom - the most stable energy state of an electron
Specific heat capacity
The energy required per unit mass to change the temperature by 1K (or 1°C); unit Jkg⁻¹K⁻¹
Specific latent heat
The energy required to change the phase per unit mass while at constant temperature- symbol L
Specific latent heat of fusion
The energy required to change unit mass of a substance from solid to liquid while at a constant temperature - Symbol L(v)
Specific latent heat of vaporisation
The energy required to change unit mass of a substance from solid to liquid while at a constant temperature - symbol L(f)
Elastic potential energy
The energy stored in an object because of its deformation
Tensile strain
The extension per unit length, a dimensionless quality
Strain
The extension per unit length, a dimensionless quantity
Hooke's law
The force applied is directly proportional to the extension of the spring unless the limit of proportionality is exceeded
Newton's law of gravitation
The force between two point masses is directly proportional to the product of the masses and inversely proportional to the square of the separation between them: F=-(GMm)/r₂
Normal contact force
The force exerted by a surface on an object, which acts perpendicularly to the surface
Pressure
The force exerted per unit cross-sectional area, measured in pascals, Pa
Electric field streingth
The force experienced per unit positive charge at that point
Stress
The force per unit cross-sectional area, measured in Pa
Tensile stress
The force per unit cross-sectional area, measured is Pa
Natural frequency
The frequency of a free oscillation
Driving frequency
The frequency with which the periodic driver force is applied to a system in forced oscillation.
Electromagnetic spectrum
The full range of frequencies of electromagnetic waves, from gamma rays to radio waves
Aphelion
The furthest point from the sun in an orbit
Hubble constant
The gradient of a best-fit line for a plot of recessional speed against distance from Earth of other galaxies
Gravitational field strength, g
The gravitational force exerted per unit mass at a point within a gravitational field
Weight
The gravitational force in an object, measured in newtons, N
Expanding Universe
The idea that the fabric of space and time is expanding in all directions and that as a result any point, in any part of the Universe, is moving away from every other point in the Universe, and the further the points are apart the faster their relative motion away from each other
Supernova
The implosion of a red supergiant at the end of its life, which leads to subsequent ejection of stellar matter into space, leaving an inert remnant core
Resonance
The increase in amplitude of a forced oscillation when the driving frequency matches the natural frequency of the oscillating system
Extension
The increase in length of an object when a tensile force is exerted on it
Gas laws
The laws governing the behaviour of ideal gases, like Boyle's law
Red shift
The lengthening of observed wavelength that occurs when a wave source is moving away from the Earth (receding), the absorption lines in its spectrum will be red-shifted
Boltmann consant
The molar gas constant R divided by the Avogrado contant N_A, a constant that relates the main kinetic energy of atoms or molecules in a gas to the gas temperature- symbol 'k'
Free oscillation
The motion of a mechanical system displaced from its equilibrium position and then allowed to oscillate without any external forces
Free fall
The motion of an object accelerating under gravity with no other force acting on it
Number density
The number of free electrons per cubic metre of a material, symbol 'n', unit m⁻³
Atomic number
The number of protons in a nucleus
Frequency (waves)
The number of wavelengths passing a given point per unit time
Kepler's first law of planetary motion
The orbit of a planet is an ellipse with the sun at one of the two foci
Planetary nebula
The outer layers of a red giant that have drifted off into space, leaving the hot core behind at the centre as a white dwarf
Wien's displacement law
The peak wavelength λ(max) at which the intensity of radiation from a black body is a maximum is inversely proportional to the absolute temperature T of the black body
Polarisation
The phenomenon in which oscillations of a transverse wave are limited to only one plane
Diffraction
The phenomenon in which waves passing through a gap or around an object spread out
Maximum (waves)
The point of greatest amplitude in an interference pattern, produced by constructive interference
Minimum (waves)
The point of least amplitude in an interference pattern, produced by destructive interference
Polycrystalline graphite
Thin layers of graphite with regularly arranged carbon atoms in different orientations
Triangle of forces
Three forces acting at a point in equilibrium, represented by the sides of the triangle
Principle of conservation of momentum
Total momentum of a system remains the same before and after a collision
Newton's third law of motion
When two objects interact, each exerts an equal but opposite force on the other during the interaction
Principle of superposition of waves
When two similar types of waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves
Ohm's law
The potential difference across a conductor is directly proportional to the current in the component as long as its temperature remains constant
Terminal p.d.
The potential difference across an electrical power source -- when there is no current this is equal to the e.m.f. minus the lost volts
Lost volts
The potential difference across the internal resistor of a source of e.m.f.
Boyle's law
The pressure of an ideal gas is inversely proportional to its volume, provided that the mass of gas and the temperature do not vary
Decay constant
The probability of decay of an individual nucleus per unit time
Radioactivity
The process by which unstable nuclei split, or decay, emitting ionising radiation (alpha particles, beta particles, and gamma rays)
Time constant
The product of capacitance and resistance, CR, for a capacitor-resistor circuit - equal to the time taken for the p.d. (or the current or the charge) to decrease to e⁻¹ (about 37%) of its initial value when the capacitor discharges through a resistor - symbol τ
Moment
The product of force and perpendicular distance from a pivot or stated point
Work
The product of force and the distance moved in the direction of the force, measured in J
Torque (of a couple)
The product of one of the forces of a couple and the perpendicular distance between the forces
Magnetic flux
The product of the component of the magnetic flux density perpendicular to a given area and that cross-sectional area: φBAcosθ
Acoustic independance
The product of the density 'p' of a substance and the speed 'c' of ultrasound in that substance- symbol Z, SI unit kgm⁻²s⁻¹
Linear momentum
The product of the mass and velocity of a particle, measured in kgms⁻¹ or Ns
Magnetic flux linkage
The product of the number of turns in a coil N and the magnetic flux φ
Piezoelectric effect
The production of an electromotive force (e.m.f.) by some crystals, such as quartz, when they are compressed, stretched, twisted, or distorted
Tension
The pulling force exerted by a string, cable, or chain on an object
Intensity (waves)
The radiant power passing through a surface per unit area -- unit Wm⁻²
Corrected count rate
The radiation count rate measured in an experiment minus the background count rate
Background radiation
The radiation emitted by the surroundings, which must be measured before radiation produced in an experiment can usefully be measured.
Activity
The rate at which nuclei decay or disintegrate in a radioactive source, measures in becquerels (Bq) or decays per second.
Acceleration of free fall
The rate if change of velocity of an object falling in a gravitational field, symbol g
Average speed
The rate of change in distance calculated over a complete journey
Angular velocity
The rate of change of angle for an object moving in a circular path- symbol ω
Newton's second law of motion
The rate of change of momentum of an object is directly proportional to the resultant force and takes place in the direction of the force
Acceleration
The rate of change of velocity, a vector quantity
Electric current
The rate of flow of charge, symbol 'I', measured in ampères, A; normally a flow of electrons in metals ore a flow of ions in electrolytes
Power
The rate of work done, measures in watts, W
Intensity reflection coefficient
The ratio of reflected intensity over incident intensity for ultrasound incident at a boundary
Young modulus
The ratio of tensile stress to tensile strain when these quantities are directly proportional to each other, measured in Pa
Efficiency
The ratio of useful output energy to total input energy, often expressed as a percentage
Hubble's law
The recessional speed 'v' of a galaxy is almost directly proportional to its distance 'd' from the Earth
Total internal reflection
The reflection of all light hitting a boundary between two media back into the original medium when the light is travelling back into the original medium when the light is travelling through the medium with the higher refractive index and the incidence angle at the boundary is greater than the critical angle
Refractive index
The refractive index of a material, n-c/v where 'c' is the speed of light through a vacuum and 'v' is the speed of light through the material
Black hole
The remnant core of a massive star after it has gone supernova and the core has collapsed so far that in order to escape it an object would need an escape velocity greater than the speed of light, and therefore nothing, not even photons, can escape
Neutron star
The remnant core of a massive star after the star has gone supernova and (if the mass of the core is greater than the Chandrasekhar limit) the core has collapsed under gravity to an extremely high density (similar to that of an atomic nucleus, ~10¹⁷kgm⁻³), as it is almost entirely made up of neutrons
Pair production
The replacement of a single photon with a particle and a corresponding antiparticle of the same total energy
Internal resistance
The resistance of a source of e.m.f. (e.g. of a cell) due to its construction, which causes a loss in energy/voltage as the charge passes through the source, symbol 'r', SI unit ohm, Ω
Drag force
The resistive force exerted by a fluid on an object moving through it
Equilibrium position (waves)
The resting position of waves or particles in an oscillation
Isotropic
The same in all directions (for example the Universe, appearing the same to any observer regardless of position)
Grating spacing
The separation between adjacent lines or slits in a diffraction grating
Blue shift
The shortening of observed wavelength that occurs when a wave source is moving towards the observer- in astronomy, if a galaxy is moving towards the Earth, the absorption lines in its spectrum will be blue-shifted, that is, moved towards the blue end of the spectrum
Nucleus
The small, positively charged region at the centre of an atom where most of the mass of the atom is concentrated
Instantaneous speed
The speed at the moment it is measured -- speed over an infinitesimal interval of time
Pythagoras' theorum
The square of the length of the hypotenuse of a right-angled triangle equals the sum of the squares of the lengths of the other two sides
Kepler's third law of planetary motion
The square of the orbital period 'T' of a planet is directly proportional to the cube of its average distance 'r' from the Sun
Root mean square speed
The square root of the mean square speed (of all the particles in a gas)
Magnetic flux density
The strength of a magnetic field- defined by the equation F/IL, where 'F' is the force acting on current-carrying conductor placed at right angles to a magnetic field, 'I' is the current in the conductor and 'L' is the length of the conductor in the magnetic field - symbol 'B', unit tesla (T)
Breaking strength
The stress value at the point of fracture, calculated by dividing the breaking force by the cross-sectional area
Internal energy
The sum of randomly distributed kinetic and potential energies of the atoms, ions, or molecules within the substance
Big bang
The theory that at a moment in the past all the matter in the Universe was contained in a singularity (at a single point), the beginning of space and time that expanded rapidly outwards
Compressive deformation
A change in the shape of an object due to compressive forces
Tensile deformation
A change in the shape of an object due to tensile forces
Battery
A collection of cells that transfers chemical energy into electrical emergy
Galaxy
A collection of stars and interstellar dust and gas bound together by their mutual gravitational force
Inelastic collision
A collision in which kinetic energy is transferred to other forms, e.g. heat
Perfectly elastic collision
A collision in which no kinetic energy is transferred
Non-ohmic component
A component that does not obey Ohm's law, e.g. filament lamp and diode
Capacitor
A component that stores charge, consisting of two plates separated by an insulator (dielectric)
Ohmic conductor
A conductor that obeys Ohm's law
Conservation of charge
A conservation law which states that electrical charge can neither be created nor destroyed - the total charge in any interaction must be the same before and after the interaction
Exponential decay
A constant-ratio process in which a quantity decreases by the same factor in equal time intervals
Threshold voltage
The minimum potential difference at which a diode begins to conduct
Electric potential
The work done by an electrical force per unit positive charge to bring a charge from infinity to a point in an electric field - unit Volt or JC⁻¹
Electric potential difference
The work done by an external force per unit positive charge to move a charge between two points in an electric field
Gravitational potential
The work done per unit mass to bring an object from infinity to a point in the gravitational field - unit Jkg⁻¹
Equation of state of an ideal gas
pV=nRT, where n is the number of moles of gas
Homogeneous
Uniform in terms of the distribution of matter across the Universe when viewed on a sufficiently large scale
Magnetic field patterns
Visual representations used in interpreting the direction and strength of magnetic fields
Series circuit
A type of electrical circuit where the components are connected end-to -end
Bacquerel
A unit of activity- one bacquerel is an activity of one decay per second
Derived unit
A unit used to represent a derived quantity, such as N for force
Escape velocity
The minimum velocity at which an object has just enough energy to leave a specified gravitational field
Excited
(an atom) \containing an electron or electrons that have absorbed energy and been boosted into a higher energy level
Impedance matching
(or acoustic matching) The use of two substances with similar acoustic impedance to minimise the reflection of ultrasound at the boundary between them
Acoustic matching
(or impedance matching) The use of two substances with similar acoustic impedance to minimise reflection of ultrasound at the boundary between them.
Frequency
(oscillations) The number of complete oscillation per unit time - unit Hertz, Hz
Nebula
(plural nebulae) A cloud of dust and gas (mainly hydrogen), often many hundreds of times larger than our Solar System
Avogadro constant
6.02x10²³, the number of atoms in 0.012kg (12g) of carbon-12; Symbol N_A
Planetary satellite
A body in orbit around a planet - it may be natural (as a moon) or artificial
Equilibrium
A body is in equilibrium when the net force and net moment acting on it are zero
Satellite
A body orbiting around a planet
Newton's first law of motion
A body will remain at rest or continue to move with constant velocity unless acted upon by a resultant force
Anode
A positively charged electrode
Cation
A positively charged ion, one which is attracted to a cathode
Proton
A positively charged particle, a hadron, found in the nucleus of atoms
Fission
A process in which a large nucleus splits into two smaller nuclei after absorbing a neutron
Fusion
A process in which two smaller nuclei join together to form one larger nucleus
Nuclear fusion
A process in which two smaller nuclei join together to form one larger nucleus
Resistance
A property of a component calculated by dividing the potential difference across it by the current in it, symbol R, unit ohm, Ω
Resistivity
A property of a material, measured in Ωm, defined as the product of the resistance of a component made of the material and its cross-sectional area divided by its length
Quantity
A property of an object, substance, or phenomenon that can be measured
Force
A push or pull on an object, measured in newtons, N
Force constant
A quantity determined by dividing the force by extension (or compression) for an object obeying Hooke's law -- called constant of proportionality, k, in Hooke's law, measured in Nm⁻¹
Derived quantity
A quantity that comes from a combination of base units
Angular frequency
A quantity used in oscillatory motion- equal to the product of frequency 'f' and 2π
Vector quantity
A quantity with magnitude (size) and direction
Scalar quantity
A quantity with magnitude (size) but no direction
Photon
A quantum of electromagnetic energy -- photon energy, E, is given by E=hf, where 'h' is the Planck constant and 'f' is the frequency of the electromagnetic radiation
Electron degeneracy pressure
A quantum-mechanical pressure created by the electrons in the core of a collapsing star due to the Pauli exclusion principle
Radiopharmaceutical
A radioisotope chemically combined with elements that will target particular tissues in order to ensure that the radioisotope reaches the correct organ or tumour for the diagnosis or treatment
Medical tracer
A radiopharmaceutical, that is, a compound labelled with a radioisotope that can be traced inside the body using a gamma camera
Chain reaction
A reaction in which the neutrons from an earlier fission stage are responsible for further fission reactions leading to an exponential growth in the rate of the reactions
Thermal equilibrium
A state in which there is no net flow of thermal energy between the objects involved, that is, objects in thermal equilibrium must be at the same temperature
Plumb-line
A string with a weight used to provide a vertical reference line
Fluid
A substance that can flow, including liquids and gases
Coolant
A substance that removes the thermal energy produced from reactions within a fission reactor
Moderator
A substance used to slow down the fast neutrons produced in fission reactions so that they can propagate the fission reaction
Radial field
A symmetrical field that diminishes with distance² from its centre, such as the gravitational field around a spherical mass or the electron field around a spherical charged object
Spectroscopy
A technique in physics in which spectral lines are identified and measured in order to identify elements present within stars
Stellar parallax
A technique used to determine the distance to stars that are relatively close to the Earth (less than 10pc) by comparing their apparent positions against distant stars 6 months apart
Celsius scale
A temperature scale with 100 degrees between the freezing point and the boiling point of pure water (at atmospheric pressure 1.01x10³ Pa), 0°C and 100°C
Wave-particle duality
A theory that states that matter has both particle and wave properties and also electromagnetic radiation has wave and particulate (photon) nature
Step-down transformer
A transformer with fewer turns on the secondary coil than on the primary coil, and a lower output voltage than input voltage
Step-up transformer
A transformer with more turns on the secondary than on the primary coil, and a higher output voltage than input voltage
Vector triangle
A triangle constructed to scale to determine the resultant of two vectors.
Parallel circuit
A type of branching electrical circuit in which there is more than one path for the current -- components in parallel have the same potential difference
Light-emitting diode
A type of diode that emits light when it conducts electricity
Photomultiplier tube
An apparatus that converts a photon of visible light into an electrical pulse, for example as a part of a gamma camera
Series
An arrangement of electrical components connected end-to-end, that means that the current is the same in each component
Ion
An atom that has either lost or gained electrons and so has a net charge
Resistor
An electrical circuit component that obeys Ohm's law, transferring electrical energy to thermal energy
Potential divider
An electrical circuit designed to divide the potential difference across two or more components (often two resistors) in order to produce a specific output
Filament lamp
An electrical component containing a narrow filament of wire that transfers electrical energy into heat and light
Thermistor
An electrical component that has a resistance that decreases as the temperature increases (a negative temperature coefficient)
Light-dependent resistor
An electrical component with a resistance that decreases as the light intensity incident on it increases
Neutron
An electrically neural particle, a hadron, found in the nucleus of atoms
Free electron
An electron in a metal that is free to move -- sometimes called a delocalised electron
Quark
An elementary particle that can exist in six forms (plus their antiparticles) and joins with other quarks to make up hadrons
Ellipse
An elongated 'circle' with two foci
De Broglie Equation
An equation relating the wavelength and the momentum of a particle λ=h/p or λ=h/mv
Grating equation
An equation that can be used to determine accurately the wavelength of monochromatic light sent through a diffraction grating, dsinθ=nλ
Wave equation
An equation that relates the frequency f in hertz, the wavelength λ in metres and the wave speed v in ms⁻¹: v=fλ
Potential divider equation
An equation with three terminals and some form of sliding contact that can be adjusted to vary the potential difference between two terminals
Red giant
An expanding star at the ends of its life, with an inert core in which fusion no longer takes place, but in which fusion of lighter elements continues in the shell around the core
Ionising radiation
Any form of radiation that can ionise atoms by removing an electron to leave a positive ion
Meson
Any hadron comprising a combination of a quark and an anti-quark
Baryon
Any hadron made with a combination of three quarks
Coulomb's law
Any two point charges exert an electrostatic (electrical) force on each other that is directly proportional to the product of their charges and inversely proportional to the square of their separation
Kirchhoff's first law
At any point in an electrical circuit, the sum of currents into that point is equal to the sum of currents out of that point, electrical charge is conserved
Tensile force
Equal and opposite forces acting on a material to stretch it
Turn-ratio equation
Equation for a transformer: V(s)/V(p)=n(s)/n(p), where output voltage is V(s), input voltage is V(p), the number of turns is the secondary coil is n(s), and number of turns in the primary coil is n(p)
Universe
Everything that exists within space and time
f
Femto, 10⁻¹⁵
Kirchhoff's second law
In a closed loop of an electrical circuit, the sum of currents into that point is equal to the sum of the e.m.f.s is equal to the sum of the p.d.s
Gradient
In a graph, the change in the vertical axis quantity divided by the corresponding change in the horizontal axis quantity
Monochromatic light
Light of a single frequency
Magnetic field lines
Lines of force drawn to represent a magnetic field pattern
Gravitational field lines
Lines of force used to map the gravitational field pattern around an object having mass
Constant velocity
Motion in which the change in the displacement per unit time stays the same
Constant speed
Motion in which the distance travelled per unit time stays the same
Collimator
Part of a gamma camera, a honeycomb of long, thin tubes made from lead that absorbs any photons arriving at an angle to the axis of the tubes so that a clear picture is obtained
Scintillator
Part of a gamma camera, often made of sodium iodide, which produces thousands of photons of visible light when struck by a single gamma photon
Antiphase
Particles oscillating completely out of step with each other (one reaches its maximum positive displacement as the other reaches its maximum negative displacement) are in antiphase
In phase
Particles oscillation perfectly in time with each other (reaching their maximum positive displacement at the same time) are in phase
Out of phase
Particles that are neither in phase, nor antiphase, are out of phase
p
Pico, 10⁻¹²
Voltage
Potential differnece
Radiation pressure
Pressure from the photons in the core of a star, which acts outwards to counteract the pressure from the gravitational force pulling the matter in the star inwards
Ductile
Property of a material that has a large plastic region in a stress-strain graph, so can be drawn into wires
Brittle
Property of a metal that does not show plastic deformation and deforms very little (if at all) under high stress
Oscillating motion
Repetitive motion of an object around its equilibrium position
Interference
Superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements from two waves
Destructive interference
Superposition of two waves in antiphase so that the waves cancel each other out and the resultant wave has smaller amplitude than the original waves
Constructive interference
Superposition of two waves in phase so that the resultant wave has greater amplitude than the original waves
Planck constant
Symbol 'h', and important constant in quantum mechanics, 6.63x10⁻³⁴Js
SI
Système International d'Unités (International System of Units)
T
Tera, 10¹²
Fundamental frequency
The lowest frequency at which an object (e.g., an air column in a pipe of a string fixed at both ends) can vibrate
Absolute zero
The lowest possible temperature, the temperature at which substances have minimum internal energy
Faraday's law
The magnitude of the induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage
Main sequence
The main period on an H-R diagram in a star's life, during which it is stable
Chandrasekhar limit
The mass of a star's core beneath which the electron degeneracy pressure is sufficient to prevent gravitational collapse, 1.44 solar masses
Rest mass
The mass of an object, such as a particle, when it is stationary
Molar mass
The mass of one mole of a substance
Density
The mass per unit volume of a substance
Amplitude (waves)
The maximum displacement from the equilibrium position (can be positive or negative)
Trough
The maximum negative amplitude of a transverse wave
Peak
The maximum positive amplitude of a transverse wave
Ultimate tensile strength
The maximum stress that a material can withstand before it breaks
Astronomical unit
The mean distance from the Earth to the Sun, i.e.150 million km or 1.5x10¹¹m
Mean square speed
The mean of the squared velocities (of all the particles in a gas)
Microwave background radiation
The microwave signal of uniform intensity detected from all directions of the sky, which fits the profile for a black body at a temperature of 2.7K
Wavelength
The minimum distance between two points oscillating in phase, for example the distance from one peak to the next or from one compression to the next
Work function
The minimum energy needed to remove a single electron from the surface of a particular metal; symbol φ, measured in J
Binding energy
The minimum energy required to completely separate a nucleus into its constituent protons and neutrons
Threshold frequency
The minimum frequency of electromagnetic radiation that will cause the emission of an electron from the surface of a particular metal - symbol f₀, measured in Hz
Timebase
The time interval represented by one horizontal square on an oscilloscope screen
Time of flight
The time taken for an object to complete its motion
Period (waves)
The time taken for one complete wavelength to pass a given point
Period (oscillations)
The time taken to complete one oscillation
Stopping distance
The total distance travelled from the time when a driver first sees a reason to stop and the time when the vehicle stops, the sum of the thinking distance and the breaking distance
Principle of conservation of energy
The total energy of a closed system remains the constant- energy cannot be created nor can it be destroyed
Nucleon number
The total number of protons and neutrons in a nucleus (also called the mass number); symbol 'A'
Luminosity
The total radiant power output of a star- symbol 'L', unit W
Polarity
The type of charge (positive or negative) or the orientation of a cell relative to a component
Archimedes' principle
The upthrust on an object in a fluid is equal to the weight of fluid it displaces
Upthrust
The upward buoyant force exerted on a body immersed in a fluid
Elastic limit
The value of stress or force beyond which elastic deformation becomes plastic deformation, and the material or object will no longer return to its original shape and size when the stress or force is removed
Limit of proportionality
The value of stress or force beyond which stress is no longer directly proportional to strain
Compressive force
Two or more forces together that reduce the length or volume of an object
Resistor circuit
Two or more resistors arranged to provide a specific resistance
Coherence
Two wave sources, or waves, that are coherent have a constant phase difference
Alpha
Α, α
Beta
Β, β
Gamma
Γ, γ
Delta
Δ, δ
Epsilon
Ε, ε
Zeta
Ζ, ζ
Eta
Η, η
Theta
Θ, θ
Iota
Ι, ι
Kappa
Κ, κ
Lambda
Λ, λ
Mu
Μ, μ
Nu
Ν, ν
Xi
Ξ, ξ
Omnicron
Ο, ο
Pi
Π, π
Rho
Ρ, ρ
Sigma
Σ, σ
Tau
Τ, τ
Upsilon
Υ, υ
Phi
Φ, φ
Chi
Χ, χ
Psi
Ψ, ψ
Omega
Ω, ω
