Definitions For Paper 2 Flashcards
Absorption coefficient
A measure of the absorption of x-ray photons by a substance also known as as attentiuon coefficient
Acoustic matching
The use of two substances with similar acoustic impedance to minimise reflection of ultrasound at the boundary between them
Activity
The rate of which nuclei decay or disintegrate in a radioactive source measured in becquerels
Acoustic impedance
The product of the density of a substance and the speed of ultrasound in that substance
Alpha radiation
Ionising radiation consisting of particles comprising two protons and two neutrons with a charge of +2e
Ampere
The current flowing in two parallel wires in a vacuum 1m apart such that there is an attractive force of 2x10^-7N per metre length of wires between them
Amplitude
The maximum displacement from the equilibrium position
Angle of incidence
The angle between the direction of travel of an incident wave and the normal at a boundary between two media
Angle of reflection
The angle between the direction of travel of a reflected wave and the normal at a boundary between two media
Anion
A negatively charged ion, one which is attracted to an anode
Annihilation
The complete destruction of a particle and its antiparticle in an interaction that releases energy in the form of identical photons
Anode
A positively charged electrode
Antiparticle
The antimatter counterpart of a particle with the opposite charge to the particle and exactly the same rest mass
Antiphase
Particles oscillating completely out of step with each other
Atomic mass unit
One atomic mass unit is one-twelfth the mass of a neutral carbon-12 atom
Atomic number
The number of protons in a nucleus Z
Attenuation
The decrease in the intensity of electromagnetic radiation as it passes through matter and/or space
Attenuation coefficient
A measure of the absorption of x-ray photons by a substance also known as absorption coefficient - m^-1
Background radiation
The radiation emitted by the surroundings, which must be measured before radiation produced in an experiment can be usefully measured
baryon
Any hadron made with a combination of three quarks
Battery
A collection of cells that transfers chemical energy into electrical energy
Becquerel
One becquerel is an activity of one decay per second
Beta decay (B-)
A neutron in an unstable nucleus decays into a proton, an electron and and electron antineutron
Beta decay (B+)
A proton in an unstable nucleus decays into a neutron, a positron and an electron neutrino
Beta radiation
Ionising radiation consisting of fast-moving electrons (B- or B+) emitted from unstable nuclei with a charge of -e or +e
Binding energy
The minimum energy required to completely separate a nucleus into its constituent protons and neutrons
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
Capacitance
The charge stored per unit potential difference across a capacitor
Capacitor
A component that stores charge, consisting of two plates plates separated by an insulator
Carbon dating
A method of determining they 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
Cathode
A negatively charged electrode
Cation
A positively charged ion, one which is attracted to a a cathode
Cell
A device that transfers chemical energy into electrical energy
Chain reaction
A reaction in which the neutrons from an earlier fission stage are responsible for future fission reactions leading to an exponential growth in the rate of the reactions
Charge carriers
A particle with charge that moves through a material to form an electric current
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
Coherence
Two waves sources or waves that are coherent have a constant phase difference
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
Compression
A moving region in which the medium is denser or has higher pressure than the surrounding medium
Conservation of charge
A conservation law which states that electric charge can neither be created more destroyed - the total charge in any interaction must be the same before and after the interaction
Constructive interference
Superposition of two waves in phase so that the resultant wave has greater amplitude than the original waves
Control rods
Rods made of a material whose nuclei readily absorb neutrons which can be moved into or out of a reactor core to ensure that exactly one slow neutron survives per fission reaction or to completely stop the fission reaction
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
Coolant
Substance that removes the thermal energy produced from reactions within a fission reactor
Corrected count rate
The radiation count rate measured in an experiment minus the background count rate
Coulomb
SI unit of electrical charge - 1 coulomb of electric charge passes a point in one second when there is an electric current of one ampere
Coulomb’s law
Any two point charges exert an electrostatic force on each other that is directly proportional to the product of their charges and inversely proportional to the square of their separation
Coupling gel
A gel with acoustic impedance similar to that of skin smeared onto the transducer and the patients skin before an ultrasound scan in order to fill air gaps and ensure that almost all the ultrasound enters he patients body
Critical angle
The angle of incidence at the boundary between two media that will produce an angle of refraction of 90 degrees
Crystallography
A method of determining the structure of a substance by studying the interference patterns produced by waves passing through a crystal of the substance
Daughter nucleus
A new nucleus formed following a radioactive decay
De broglie equation
An equation relating the wavelength and momentum of a particle
Decay constant
The probability of decay of an individual nucleus per unit time
Density
The mass per unit volume of a substance
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
Diffraction
The phenomenon in which waves passing through a gap or around an obstacle spread out
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
Diode
A semiconductor component that allows surrender only in one particular direction
Displacement
He distance from the equilibrium position in a particular direction - displacement is a vector can be positive or negative
Electric charge
A physical property either positive or negative measured in coulombs or as a relative charge
Electric current
The rate of flow of charge measured in ampere: normally a flow of electrons in metals or. A flow of ions in electrolytes
Electric field strength
The force experienced per unit positive charge at the point
Electric potential
The work done by an external force per unit positive charge to bring a charge from infinity to a point in an electric field
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
Electromagnetic spectrum
The full range of frequencies of electromagnetic eaves , from gamma rays to radio waves
Electrolyte
A liquid containing ions that are free to move and so to conduct electricity
electromagnetic wave
Transverse waves with oscillating electric and magnetic field components such as light and X-rays that do not need a medium to propagate they travel at a speed of light 3x10^8 ms^-1 in a vacuum
Electromotive force
The energy transferred from chemical to electrical energy per unit charge
Electron gun
A device that uses a large accelerating potential difference to produce narrow beam of electrons
Electronvolt
A derived unit of energy used for subatomic particles and photons
- the energy transferred to or form an electron whin it passes through potential difference of 1 volt = 1eV
Elementary charge
The electric charge equivalent to the charge on a proton = e
Elementary particle
A fundamental particle
Energy
The capacity for doing work - J
Equation of state of an ideal gas
pV = nRT, where n is the number of moles of gas
Equilibrium position
The resting position of waves or particles in an oscillation
Exponential decay
A constant-ratio process in which a quantity decreases by the same factor in equal time intervals
Extension
The increase in length of an object when a tensile force is exerted on it
Faraday’s law
The magnitude of the induced e.m.f is directly proportional to the rate of change of magnetic flux linkage
Filament lamp
An electrical component containing a narrow filament of wire that transfers electrical energy into heat and light
Fission
A process in which a large nucleus splits into two smaller nuclei after absorbing a neutron
Flemings left hand rule
A mnemonic for the direction of the force experienced by a current-carrying wire placed perpendicular to the external magnetic field: on the left hand, the fist finger gives the direction of the external magnetic field, the second finger gives the direction of the conventional current and the thumb gives the direction of motion in the wire
Free electron
An electron in a kernel that s not bound to an ton and is free to move - delocalised electron
Frequency
The number of wavelengths passing a given point per unit time
Fundamental frequency
The lowest frequency at which an object can vibrate
Fundamental mode of vibration
A vibration at the fundamental frequency
Fundamental particle
A particle that has no internal structure and hence cannot be split into smaller particles
Fusion
A process in which two smaller nuclei join together to form one larger nucleus
Gamma radiation
Ionising radiation consisting of high-energy photons with wavelengths less than about 10^-13m
Gamma rays
Short-wavelength electromagnetic waves with wavelengths from 10^-10m to 10^-16m
Gold-leaf electroscope
A device with a metallic stem and a gold leaf that can be used to identify and measure electric charge
Hadron
A particle or antiparticle that is affected by the strong nuclear force and if charged by the electromagnetic force
Half-life
The average time it takes for half the number of active nuclei in a sample of an isotope to decay
Harmonic
A whole-number multiple of the fundamental frequency
Impedance matching
The use of two substances with similar acoustic impedance to minimise reflection of ultrasound at the boundary between them
In phase
Particles oscillating perfectly in time with each other (max displacement at the same time) are in phase
Induced fission
Nucleus fission occurring when a nucleus becomes unstable on absorbing another particle
Infrared waves
Electromagnetic waves, with wavelengths from 10^-3m to 7x10^-7m
Intensity
The radiant power passing through a surface per unit area unit Wm^-2
Intensity reflection coefficient
The ratio of reflected intensity over incident intensity for ultrasound incident at a boundary
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 the two waves
Interference pattern
A pattern of constructive and destructive interference formed as waves overlap
Internal resistance
The resistance of a source of e.m.f due to its construction which causes a loss in voltage as the charge passes through the source
Ion
An atom that has either lost or gained electrons and so has a net charge
Ionic solution
An ionic compound dissolved in a liquid to form an electrolyte
Ionising radiation
Any form of radiation that can ionise atoms by removing an electron to leave a positive ion
Isotopes
Nuclei of the same element that have the same atomic number (protons) but different nucleon numbers (neutrons)
I-V characteristic
A description of the relationship between the electric current in a component and the potential difference across it - graph
Kilowatt-hour
A derived unit of energy - paying for electrical energy
Kirchoff’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
Kirchoffs second law
In a closed loop of an electrical circuit the sum of e.m.f.s is equal to the sum of the p.d.s
Law of reflection
The angle of incidence is equal to the angle of reflection
Lepton
A fundamental particle or antiparticle that is not affected by the strong nucleus force - an electron
Light-dependent resistor
An electrical component with a resistance that decreases as the light intensity incident on it increases
Light-emitting diode
A type of diode hat emits light when it conducts electricity
Loading
Connecting a component or a device across the terminals of a source of e.m.f. Or across another component
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
Lost volts
The potential difference across the internal resistor of a source of e.m.f
Magnetic flux
The product of the component of the magnetic flux density perpendicular to a given area and the cross-sectional area
Magnetic flux density
The strength of a magnetic field defined by the equation F/IL
Lenz’s law
The direction of the induced e.m.f. Is always such to oppose the change producing it
Magnetic flux linkage
The product of the number of turns in a coil and the magnetic flux
Mass defect
The difference between the mass of a nucleus and the mass of its completely separated constituent nucleons
Maximum (waves)
The point of greatest amplitude in an interference pattern produced by constructive interference
Medical tracer
A radiopharmaceutical - a compound labelled with a radioisotope that vanishes be traces inside the body with a gamma camera
Meson
Any hadron comprising a combination of a quark and an anti-quark
Microwaves
Long-wavelength electromagnetic waves 10^-1m to 10^-3 m
Minimum (waves )
The point of least amplitude in an interference pattern produced by destructive interference
Moderator
A substance used to slow down the fast neutrons produced in fission reactions so that they can propagate the fission reaction
Monochromatic light
Light of a single frequency
Negative (charge)
One tube of electric charge - attract positive charges and repel negative charge
Neutrino
A lepton (fundamental particle) that carried no charge and may have a tiny mass.
Neutron
An electrically neutral particle (hadron) found in the nuclei’s of atoms
Node
For a stationary wave, a point where the amplitude is always zero
Non-ohmic component
A component that does not obeys ohms law e,a filament lap and diode
Normal
An imaginary line perpendicular to a surface such as the boundary between one medium to another
Nucleon
A particle in the nucleus of an atom either a proton or a neutron
Nucleon number
Te total number of protons and neutrons in a nucleus - A
Nucleus
The small, positively charged region at the centre of an atom where most of the mass of the atoms is concentrated
Number density
The number of free electrons per cubic metre of material - n and unit = m^-3
Ohm
The derived SI unit if resistance - the resistance of a component has a potential difference of 1V per ampere
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
Ohmic conductor
A conductor that obeys ohm’s law
Optical fibre
A fibre made of glass designed with a varying refractive index in order to totally internal reflect pulses of visible or infrared light travelling through it
Oscilloscope
An instrument that displays n electrical signal as a voltage against time trace on screen
Out of phase
Particles are neither in phases nor antiphase
Pair production
The replacement of a single photon with a particle and a corresponding antiparticle of the same total energy
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
Parent nucleus
A nucleus before the occurrence of radioactive decay
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 - transverse waves reflect off a surface
Path difference
The difference in the distance travelled by two waves from their source to a specific point
Peak
The maximum positive amplitude of a transverse wave
Period
The time taken for one complete wavelength to pass a given point
Phase difference
The difference between the displacements of particles along a wave
Photoelectric effect
The emission of photoelectrons from a metal surface when electromagnetic radiation above a threshold frequency is incident on the metal
Photoelectrons
Electrons emitted from the surface of a metal by the photoelectric effect
Photomultiplier tube
An apparatus that converts a photon of visible light into an electrical pulse - part of gamma camera
Photon
A quantum of electromagnetic energy - E=hf
Piezoelectric effect
The production of an electromotive force by some crystals, such as quartz, when they are compressed, stretched, twisted or distorted
Plane polarised
A transverse wave in the oscillations are limited to only one plane
Polycrystalline graphite
Thin layers of graphite with regularly arranged carbon atoms in different orientations
Positive (charge)
One type of electric charge - attract negative charges and repel positive charges
Positron
The antiparticle of the electron
Potential difference
The energy transferred from electrical energy to together forms per unit charge
Potential divider
An electrical circuit designed to divide the potential difference across two or more components in order to produce a specific output
Potentiometer
An electrical component with three terminals and some form sliding contact that can be adjusted to vary the potential difference between two of the terminals
Principle of superposition of waves
When two similar types of waves meet at a point the resultant displacement at that point us equal to the sum of the displacements of the individual waves
Progressive waves
A wave in which the peaks and troughs, or compressions and rare fractions, move through the medium as energy is transferred
Proton
A positively charges particle (hadron) found in the nucleus of atoms
Proton number
The atomic number the number of protons in a nucleus -Z
P-waves
Primary waves - longitudinal waves that travel through the earth from an earthquake
Quark
An elementary particle that can exist is 6 forms and joins with other quarks to form hadrons
Quantisation
The availability of some quantities such as energy or charge
Radial field
A symmetrical field that diminishes with distance^2 from its centre (gravitational field around a spherical mass) (electrical field around a spherical charged object)
Radioactivity
The process by which unstable nuclei split or decay emitting ionising radiation
Radiopharmaceutical
A radioisotope chemically combined with elements that will target tissues in order to ensure that the radioisotope reaches the correct organ or tumour for diagnosis or treatment
Radio waves
Long-wavelength electromagnetic waves, wavelength greater than 10^-1m
Rarefraction
A moving region in which the medium is less dense or has less power than the surrounding medium
Ray
A line representing the direction of energy transfer of a wave, perpendicular to the wavefronts
Reflection
The change in direction of a wave at a boundary between two different media so that the wave remains in the original medium
Refraction
The change in direction of a wave as it changes speed when it passes from one medium to another
Relative charge
A simplified measurement of the electric charge of a particle or object measured in multiples of elementary charge
Resistance
A property of a component calculated by dividing the potential difference across it by the current in it
Resistivity
A property of a material defined as the product of the resistance of a component made of the material and its cross-sectional area divided by its length
Resistor
An electrical component that obeys ohm’s law transferring electrical energy to thermal energy
Resistor circuit
Two or more resistors arranged to provide a specific resistance
Right-hand grip rule
For a current carrying wire, thumb points in the direction of the conventional current and the direction of the field id given by the direction in which the fingers of the right hand would curl round the wire
Scintillator
Part of a gamma camera - made of sodium iodide- produces thousands of photons of visible light when struck by a single gamma photon
Semiconductor
A material with a lower number density than a typical conductor
Series
An arrangement of electrical components end-to-end that means that the current is the same,e in each component
Series circuit
A type of electrical circuit where the components are connected end-to-end
Standard model
The current theory of particle physics that deals with elementary particles (quarks and electrons) and their interactions
Standing wave
A wave that remains in a constant position with no net transfer of energy and is characterised by its nodes and antinodes
Stationary wave
A wave that remains in a constant position with non net transfer of energy and is characterised by nodes and antinodes
Step-down transformer
A transformer with fewer turns on the secondary 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
Strong nuclear force
One of the four fundamental forces in nature acting on hadrons and holding nuclei together
Superconductivity
A phenomenon in which the resistivity of a material fall to almost zero when the material is cooled below a certain temperature
Superposition
Overlap of two waves at a point in space
S-waves
Secondary-waves - transverse waves that travel through the earth from an earthquake
Target metal
A metal with a high melting point used for the anode in an x-ray tube
Terminal p.d.
The potential difference across an electrical power source - when there is no current this is equal to the e.m.f. of the source but if there is a current in the source this is equal to the e.m.f. minus the lost volts
Thermal neutron
A neutron in a fission reactor with mean kinetic energy similar to the thermal energy of particles in the reactor core - slow neutron
Thermionic emission
The emission of electrons from the surface of a heated piece of metal or hot metal wire
Thermistor
An electrical component that has a resistance that decreases as the temperature increases
Threshold frequency
The minimum frequency of the electromagnetic radiation that will cause the emission of an electron from the surface of a particular metal
Threshold voltage
The minimum potential trial difference at which a diode begins to conduct
Time constant
The product of a capacitance and resistance - regulating to the time taken for the p.d. to decrease to e^-1 of its initial value when the capacitor discharges through a resistor
Total internal reflection
The reflection of all light hitting a boundary between two media back into the original medium when the light is travelling through the medium with the higher refractive index and the incidence angle art the boundary is greater than the critical angle
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
Trough
The maximum negative amplitude of a transverse wave
Ultraviolet
Electromagnetic waves with wavelengths form 4x10^-7m to 10^-8m
Ultrasound transducer
A device used both to generate and ti receive ultrasound which changes electrical energy into sound and sound into electrical energy
Unpolarised
Description of a transverse wave in which the oscillations occur in many planes
Velocity selector
A device that used both electric and angelic fields to select charged particles of specific velocity
Visible light
Electromagnetic waves with wavelengths from 4x10^-7m to 7x10^-7m
Volt
The derived SI unit of potential difference and electromotive force defined as the energy transferred per unit charge
Wave profile
A graph showing the displacement of the particle in the wave against the distance along the wave
Wave source
A source of waves such as light or sound - the object moving relative to an observer of the Doppler effect
Wave speed
The distance travelled by the wave per unit time
Wavefront
A line of points in phase with each other in a wave, perpendicular to the direction of energy transfer
Wavelength
The minimum distance between two points oscillating in phase
Wave-particle duality
A theory that states that matter has both particle and wave properties ad also electromagnetic radiation has wave and photon nature
Weak nuclear force
On of the four fundamental forces in nature, responsible for inducing beta-decay within unstable nuclei
Work function
The minimum energy needed to remove a single electron from the surface of a particular metal
X-rays
Short wavelength from 10^-8m to 10^-13 m which an be used in medical imaging
X-ray tube
A piece of equipment that produces x-ray photons by firing electrons form a heated cathode across a large p.d. in an evacuated tube
X-ray photons
Produced. When the electrons are decelerated by hitting the target metal of an anode
Rest mass
The mass of an object, such as a particle, when it is stationary
Semiconductor
A material with a lower number density than a typical conductor
