All definitions Flashcards
Angular displacement
The angle through which an onbject moves in a circle
Radian
One radian is the angle subtended at the centre of a circle by an arc of length equal to the radius of the circle
Angular velocity
The rate of the change of the angular position of an object as it moves along a curved path
Newtons first law
An object will remain at rest or keep travelling at constant velocity unless it is acted on by a resultant force
Centripetal force
The resultant force acting on an object moving in a circle it is always derected towards the centre of the circle
Newtons secound law
The resultant force acting on an object is equal to the rate of change of its mommentum. The resultant force and the change in momentum are in the same direction.
Absolute scale
A scale of temperature
Absoulte zero
The temperature at which a system has minimum internal energy:equivalent to -273.14 degress c
Absorpution line spectrum
A dark line of a unique wavelength seen in a contunuous spectrum
Acoustic impendance
Acoustic impendance is the product of the density of a substace and the speed of sound in that substance
Activity
The rate of decay o disinitergration of nuclei in a radioactive sample
Amplitude
The maximum displacement of a particle from its equilibrium position
amplitude modulation
A form of modulation in which the signal causes variations in the amplitude of a carrier wave.
Analogue signal
A signal that is continuously variable, having a continuum of possible values.
analogue-to-digital conversion (ADC)
Conversion of a continuous analogue signal to discrete digital numbers.
angular frequency
The frequency of a sinusoidal oscillation expressed in radians per secound.
Atomic mass unit
A unit of mass approcimately equal to 1.6661x10-27 kg. The mass of an atom of carbon 12 is 12atomic uni mass exactly
attenuation
The gradual loss in strength or intenstiy of a signal
Avogadro constance
The number of particles in one mole of any substance, denoted NA (the A is subscript)
Band theory
The idea that electrons in solid or liquid can have energies within certain ranges or bands, between whicha re forbidden values.
Bandwidth (communication)
A measure of the width of a range of frequencies being transmitted.
Binding energy
The minimum external energy required to seperate all the neutrons and protons of a nucleus.
bit
A basic unit of informatino storage, the amount of information stored by a device that exsists in only two distinct states, ususally given as the binary digits 0 and 1
Boltzmann constant
A fundamental constant, which is equal to the ideal gas divided by avagadro constant
Boyle’s law
The pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature of the gas remiains the same.
braking radiation
X-Rays produced when electrons are decelerated (also clled bremsstrahlung radiation)
carrier wave
A waveform (usually sinusoidal) which is modulated by an input signal to carry information
characeteristic radiation
very intense X-rays produced in an X-ray tube, having specific wavelengths that depends on the target metal.
Charge carrier
Any charge particle sucha as an electron responsible for a current
Charles’s law
The vloume occupied by a gas at constant pressure is directly proportional to its thermodynamic (absolute) temperature
closed system
A system of interacting objects in which there are no external forces.
coaxial cable
an electrical cable with an inner conductor surrounding by a tubular inisulating layer and an outside conducting layer.
coherent
Two sources are coherent when they emit waves with a constant phase difference.
collimated beam
A paralled-sided beam of radiation.
compression
A region in a sound wave where the air pressure is greater than its mean value.
Compressive
Describes a force that squeezes an object
computerised axial tomography
A technique in whihc X-rays are used to image the human body in order to produce a computerised 3-D image.
conduction band
A range of electrons energies in a solid; electrons in the conduction band are free to move throughout the material.
Conservation of momentum
In a closed system, when bodies interact, the total momentum in any specified direction remains constant.
constructive interference
when two waves reinforce to give increased amplitude
contact force
the force a object exerts on another with which it is in contact
contrast
In a high-constrast image, there is a big difference in brightness between bright and dark areas.
Contrast media
Materials such as barium that easily absorb X-Rays. A contrast medium is used to reveal te outlnes or edges of soft tissues in an X-Ray image.
coulomb
The SI unit of electrical charge (abbreviated to C)
coulomb’s law
Any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them.
count rate
the number of particles (alpha or beta) or gamma-ray photons decteded per unit time by a Geiger-Muller tube. Count rate is always a fractino of the activity of a sample
couple
A pair of equal and antiparallel forces having a turning effect but no resultant force
Damped
Describes an oscillatory motion in which the amplitude decreases with time due to energy losses
de Brogli wavelength
The wavelength associated with a moving particle
Decay constant
It is the probability of an individual nucleus decaying per unit time interval
descibel
A logarithmic unit of measurements that expresses the realtive size of two powers.
density
The mass per unit volume of a material
destructive interference
When two waves cancel to give reduced amplitude
diffraction
the spreading of a wave when it passes through a gap or past the edge of an object
digital signal
a signal that has only a few possible values, often onyl two
digital-to-analogue conversino (DAC)
conversion of a series of digital numbers into a contiuous analogue signal.
dispersion
the splitting of light into its different wavelengths
doppler effect
The change in frequency or wavelength of a wave observed when the source of the wave is moving towards or away from the observer (or the observer is moving realtive to the sourcce))
e.m.f
The total work done when unit charge is moved round a complete circuit
Einstein relation
This refers to the eqatuion for the energy of a photon E=hf
Elastic limit
The values of stress beyound which an object will not return to its original dimensions
Elastic potential energy
Energy stored in a stretch or compressed material
Electrical charge
A property of a body that gives rise to a force on the body when it is within an electric field
electric field
A region in which a charged body experiences a force
Electric field strength
the force per unit positive charge at a point
electrical potential
The erngy per unit charge due to a charged body’s position in an electic field
electrical resistance
The ratio of potential difference to current
Electrolyte
An electrically conducting solution. The conductino is due to positive and negative ions in the solution
Electromagnetic spectrum
The family of waves that travel through a vacuum at speed of 3x10^8
electronvolt
The erngy gained by an electron travelling trhough a p.d. of 1 volt
Elementary charge
The smallest unit of charge that a particle or an object can have.
emission line spectrum
a sharp and bright line of a unique wavelenth seen in a spectrum
energy band
A range of permutted electron energies in a solid
energy level
A quantised energy state of an electron in an atom
evaporation
the process by which a liquid becomes a gas at a temperature below its boiling point
exponetial decay
describes the decrease of a quantity where the rate of decrease is proportional to the value of the quanity
farad
the unit of capacitance
Faraday’s law of electromagnetic induction
THe induced e.m.f is propotional to the rate of change of magnetic flux linkage
field line
lines drawn to represent the strength and direction of a field of a force
first law of thermodynamic
The increase in internal energy of a body is equal to the thermal energy transferred to it by heating plus the mechaniacl work done on it.
Fleming’s left-hand (motor) rule
This rule is used to predict the force experienced by a current-carrying conductor placed in an external magnetic field: Thumb–> motion
First finger –> magnetic field
Secound finger –> conventional current
Flemming right hand (generator) rule
This rule is used to predict the direction of the induced current or e.m.f. in a conductor moved at right angles to a magnetic field:
Thumb–> motion
First finger –> magnetic field
Secound finger –> conventional current
forbidden gap
A range of energy values which an electron in a solid cannot have
Force constant
THe ratio of force to extension for a spring or a wire
forced oscilation
An oscillation caused by an external driving force; the frequency is determined by the driving force, and is no the natural frequency of the oscillator
Free oscillation
An oscillation that is at its natural frequency of the oscilation
Frequency
the number of oscillations per unit time
frequency modulation
A form of modulation in which the signal causes variations in the frequency of a carrier wave.
Fundamental frequency
The lowest-frequency stationary wave for a particular system
gain
the voltage gain of an amplifier is the ratio of the output voltage to the input voltage
geostationary orbit
The orbit of an artifiial satellite which has a period equal to one day so that the satellite remains above the same point on the Earth’s equator. From earth the satellite appears to be stationary.
Gravitational field
A region where any object with mass experiences a force.
gravitational field strength
The gravitational force experienced by an object per unit mass
gravitational potential
The gravitational potential energy per unit mass at a point in a gravitational field
gravitational potential energy
The energy a body has due to its position in a gravitational field.
ground state
the lowerst energy state that can be occupied by an electron in an atom
half-life
The mean time taken for half the number of active nuclei in a radioactive sample to decay
half-thickness
The mean thickness of an absorbing material required to reduce the intensity of radiation by half
hall effect
THe production of a voltage across a conductor when a current flows through the conductor at right angles to a magnetic field
Hall voltage
The voltage produced across a conductor when a current flows through the conductor at right angles to a magnetic fiels; used ni a hall probe to measuer B
harmonic
a wave of frequency n times the fundamental frequency, where n is an interger
Hooke’s Law
The extension produced in an object is proportional to the force producing it.
idea gas
a gas that behaves according to the ideal gas equation Pv=nRT
image intensifier
A device used to change a low-intensity X-ray image into a bright visual image.
impedance matching
The reduction in intensity of ultrasound reflected at the boundary between two substances, achived when two substances have similar acoustic impedances
inelastic
A collision is inelastic when kinetic energy is not conserved; some is transferred to other forms such as heat. Momentum and total energy are always conserved.
inertia
A measure of the mass of an object. A massive object has a large inertia
instantaneous speed
The speed of an object measured over a very short period of time
intensity
The power transimitted normally through a surface per unit area
interference
The formation of points of cancellation and reinforcement where two coheret waves pass though each other.
internal energy
The sum of the random distibution of kinetic and potential enegies of the atoms or molecules in a system
internal resistance
The resistance of an e.m.f. source. The internal resistance of a battery is due to the cheicmals within it.
intrinsic semiconductor
A pure substance whose resistivity is inetermediate between that of a conductor and an insulator.
inverting amplifier
A circuit, involving the use of an amplifier, where the output is 180 degress out of phase with the input.
kinetic theory of gases
A model based on the microscopic motion of atoms or molecules of a gas
Kirchoff’s first law
The sum of the currents entering any point (or junction) in a circuit is equal to the sum of the currents leaving that same pont. This law represents the conservation of charge
Kirchhoff’s secound law
The sum of the e.m.f.s round a closed loop in a circuit is equal to the sum of p.d.s in that same loop
Larmor frequency
The frequncy of precession of nucleus in an external magnetic field
Lenz’s law
An induced current or e.m.f is in a direction so as to produce effects which oppose the change producing it.
light-depending resistor (LDR)
A resistor whose resistance decreases as the intensity of light falling on it increases.
light-emitting diode (LED)
A semiconductor component that emits light when it conducts electricity.
linear momentum
THe product of an object’s mass and its velocity
longitudinal wave
A wave in which the particles of the meium oscillate along the direction in which the wave travels.
lost volts
the difference between the e.m.f. and the terminal p.d. in a circuit. It is equal to the voltage across the internal resistance.
magnetic field
A force field in which a magnet, a wire carrying a current, r a moving charge experiences a force
magnetic flux
The product of magnetic flux density normal to a circuit and the cross-sectionaal area of the circuit.
magnetic flux density
The strength of a magnetic field. defined by the equation F/IL where;
F= force exsperiance by a conducto in the magnetic field
I= the current in the conductor
L= the length of the conductor in the magnetic field (the conductor is at a right angle to the field)
magnetic flux linkage
the product of magntic flux and the number of turns
magnetic resonance imaging
A medical imaging techinque which uses nuclear magnetic resonace.
mass
A measure of the amount of matter within an object
mass defect
the difference between the total mass of the individual, separate nucleons and the mass of the nucleus.
mass excess
the difference between the mass of a nucleide and its mass number
microwave link
a communications system that uses a beam of radio wave in the microwave frequency range to transmit audio, data or video informtion.
modulation
the process of using one waveform to alter the frequency, amplitude or phase of another waveform.
mole
THe amount of matter which contains 6.02 x10^23 particles.
monochromatic
describes light of a single frequency
natural frequency
The unforced frequency of oscillation of a freely oscillating object
negative feedback
The output of a system is used to oppose changes to the input of the system, with the result that the changes are reduced.
newtons first law of motion
An object will remain at rest or keep ttravelling at constant velocity unless it is acted on by a resultatn force.
newtons’s law of gravitation
any two point masses attract each other with a force that is directly proportional to the product of their masses and invercely propotional to the square of the sepreation
newtons’s secoud law of motion
the resultant force acting on an object is equal to the rate of change of its momentum. the resutant force and the change in the momentum are in the same direction.
newtons third law of motion
when two bodies inreact, the forces they exert on eachother are equal and opposite.
node
A point on a statinoary wave with zero amplitude
noise
An unwanted random addition to a transmitted signal
non-inverting amplifier
a citcuit, involving the use of an amplifier, in which the output is in phase with the input.
nuclear fission
THe splitting of a nucleus into two large fragments and a small number of neutrons
nuclear fusion
A nuclear reaction in which two light nuclei join together to form a heavier but more stable nucleus.
nuclear magneti resonance
A process in which radio wave absorbed or emitted by nuclei spinning in a magnetic field
nuclear model of the atom
a model of the atom in which negative charges are distributed outside a tiny nucleus of positive charge
nucleon number
the number of neutrons and protons in the nucelus of an atom
nucleon
A particle found in an atomic nucleus
nucleus
the tiny central region of the atom that contains most of the mass of the atom and all of its positive charge
nuclide
a specific combination of protons and neutrons in a nucleus
number density
the number of particles such as free electrons per unit volume in a material
Ohm’s law
The current in a metallic conducto is directly proportional to the potnetial difference across its ends, provided its temperature remains constant
operational amplifier (op-amp)
A high-gain electronic d.c. voltage amplifier with differential inputs and, usually, a single output
optic fibre
A glass or plastic fibre that caries light along its length
oscillation
A repetitive back-and-forth or up-and-down motion
path difference
the difference in the distances travelled by two waves from coherent sources at a partiular point
perfectly elastic
A collision is perfectly elastic when kinetic energy is conserved, momnetum and total energy are always conserved.
period
The time taken by an object (e.g.plant) to complete one cycle (e.g. an orbit). The period is also the time taken for one complete oscillation of a vibrating object
phase
refers to the point that an oscillating mass has reached in a complete cycle
phase difference
THe difference in the phase of two oscillatin paricles, expressed in degress or radians
phottoelectric effect
An interaction between a photon and an electron in an atom, in which the electron is removed from the atom.
piezo-electric crystal
A material that produces an e.m.f. when it is stressed, causing its shape to change. Also, when a voltage is applied across it in one direction, it changes its dimensions slightly
piezo-electric effect
The production of ane.m.f between the faces of a crystal when the crystal is compressed
planck constant
The constant which links the energy of a photon and ts frequency, in the equation
plum-pudding model
A model of the atom in which neagtive charges are distributed throughout a sphere of positvei charge
positron
an anti-electron
potential difference (p.d.)
The enrgy lost per unit charge by charges passing through a component
potential divider
A circuit in which two or more components are connected in series t a supply. The output voltage from the circuit is taken across one of the components.
potentiometer
A circuit which allows the measurement of an e.m.f. by comparison with a known e.m.f.
precession
the movement of the axis of a spinning object (proton) arouond another axis
principle of conervatino of energy
The idea that, within a closed system, the total aount of energy in all its forms is unchaged during any change.
princple of moments
for an object in equilibrium, the sum of clockwise moments about a point is equal to the sum of the anticlockwise moments about the same point.
principle of superposition
When two or more waves meet at a point, the resultant displacement is the sum of the displacements of the individual wave.
progressive wave
a wave that carries energy from one place to another
range
The horizontal distance covered by an object.
rarefaction
A region in a sound wave where the air pressure is less that its mean value.
rectification
The process of converting alternating current into direct current
red shift
The change in frequency or wavelength of a spectral line observed when the souce of light is moving away from the observer
regeneration
Restoration of a signal to its original form, usually by temoving or reducing nosie and increasing signal strength
relaxation time
the time taken for a nucleus or other exited system to fall back to a lower energy state.
relay
an electricaly operated switch caused to open and close by current in a coil
repeated
An electronic device that receives a signal and retransmits it.
resistivity
A propoerty of a material, a measure of its electrical resistance
resonance
The forced motion of an oscillator characterised by maximum amplitude when the forcing frequency matches the oscillator’s natural frequency. A system absorbs maximum energy from a source when the source frequency is equal to the natural frequency of the system
right-hand grip rule
A rule for finding the direction of the magnetic field a solenoid. If the right hand grips the solenoid with the fingers follwoing the direction of the conventional current around the solenoid, then the thumb points in the direction of the magnetic field.
sampling
Taking the value of a continuous signal at regular intervals
semiconductor diode
An electrical component made from a semiconductor material that only conduct in one direction. A diode in ‘recerse bias’ has an infinte resistance.
sensor
A device that produces an output (usually a voltage) in response to an input.
series
A term used when components are connected end-to-end in a circuit
sharpness
The degree of resolution in an image, which determines the smallest item that can be identified
simple harmonic motion
motion of an oscillator in which its acceleration is directly propotional to its displacement from its equilibrium position and is directed towards that position
solenoid
A long current-carrying coil used to generate a uniform magnetic field within its core.
specific heat capacity
The energy required per unit mass of a substance to raise its temperature by 1k
specific latent heat of fusion
The energy required per unit mass of a substance to change it from solid to liquid without a change in temperature
specific latent heat of vaporisation
The energy required per unit mass of a substance to change it from liquid to gas without a change in temperature
spin
A fundamental property of a subatomic particles which is conserved during atomic and nuclear reactions.
stationary wave
A wave pattern produced when two progressive waves of the same frequency travelling in opposite directions combine. it is characterised by noes and antinodes. Also know as a standing wave.
Strain energy
The the potential energy stored in an object when it is deformed eleastically.
strain gauge
A device that contains a fine wire sealed in plastic. Its electrical resistance changes when the object to which it is attatched changes shape.
terminal p.d.
The potential difference across an external resistor connected to an e.m.f. source
terminal velocity
the maximum velocity of an object travelling though a fluid. The resultant force on the object is zero
tesla
The SI unit of magetic flux density
thermal energy
Energy transferred from one object to another because of a temperature difference; another term for heat energy.
thermal equilibrium
A condition when two or more object in contact have the same temperature so that there is no net flow of energy between them.
thermistor
A device whose electrical resistance changes when its temperature changes.
thermocouple
A device consisting of wire of two different metals acorss which an e.m.f. is produced when the two junctions of the wires are at different temperatres.
thermodynamic scale
A temperature scale in which temperarture is measured in kelvin
threshold frequency
The minimum frequency of electromagnetic radiation that will eject electrons from the surface of a metal
threshold voltage
The minimum forward bias voltage across a light-emitting diode (LED) when it starts to conduct and emit light.
time constant
The time taken for the current, stored charge or p.d. to fall to 1/e (about 37%) of its original value when a capcitor discharges through a resistor. It is also equal to the product of capacitance and resistance.
tracers
radioactive substances used to investigate the functions of organs of the body.
transducer
A general term used for any device that changes from one form of energy into another.
transition
When an electron makes a ‘jump’ between two energy levels.
transverse wave
A wave in which the particles of the mediiumm oscillate at right angles to the direction in which the wave travels.
turns-ratio equation
An equation relating the ratio of voltage to the ratio of numbers of turns on the two coils of a transformers.
upthrust
The upwards force that a liquid eerts on a body floating or immersed in a liquid
valence band
A range of electron energies in a solid; electrons in the valence band are bound to individual atoms.
Virtual earth approximation
An approximation in which the two inputs of an op-amp are nearly at the same potential.
viscous forces
Forces that act on a body moving through a fluid that are caused by the resistance of the fluid.
voxel
A small cube in a three-dimension image, the equivalent of pixel in a two-dimensional image.
wire-pair
A type of electrical wiring in which the two conductos needed to carry a signal are placed close together.
work function
the minimum energy required by a single electron to escape a metal surface.
X-ray tube
A device that produces X-ray when accelerated electron hit a target metal
