PH2 DEFINITIONS

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• Created by: Gen Kirk
• Created on: 08-01-16 09:22
COULOMB
this is the amount of charge that passes a point when a current of 1 amp flows for 1 second
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AMPERE
one amp of current is a coulomb of charge being moved, per second
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ELECTRIC CURRENT
the rate of flow of charge past a point
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OHM'S LAW
this states that for a metallic conductor at a constant temperature, the current flowing through it, is directly proportional to the P.D. across it
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RESISTANCE
this is the P.D. placed across the device divided by the current flowing through it
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THE OHM
is the resistance of a conductor when a current of 1 amp flows, when a P.D. of 1 volt is applied to it
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POTENTIAL DIFFERENCE
this is the electrical potential energy changed to other forms, when unit charge moves between two points
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THE VOLT
this is the potential between two points in a circuit, if 1 joule of energy is converted into other forms when 1 coulomb of charge moves between the points
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RESISTIVITY
this is the resistance of a sample of material of unit cross sectional area and unit length
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SUPERCONDUCTIVITY
the term given to the phenomenon, by which a metallic conductor behaves as if it has zero resistance
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SUPERCONDUCTING
the adjective used to describe materials that are below their transition temperature and therefore the resistance of which, it virtually zero.
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TRANSITION TEMPERATURE
that temperature, below which, the resistance of the metal suddenly drops to zero
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THE LAW OF CONSERVATION OF CHARGE
electrical charge cannot be created or destroyed. As a consequence to this the current flowing to any point is equal to that flowing from it
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THE ELECTRO-MOTIVE FORCE or E.M.F. of a cell
the energy transferred to other forms, throughout the circuit, when unit charge passes through the cell
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TRANSVERSE WAVE
in a transverse wave, the oscillations of the particles or field are perpendicular (right angle) to the direction of propagation of energy
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LONGITUDINAL WAVE
in a longitudinal wave the oscillation of the particles are parallel to the direction of propagation of energy
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POLARISATION
energy in the form of waves are said y be polarised, if the oscillations of each photon are orientated into the same place (note: only transverse waves can be polarised)
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DISPLACEMENT (waves)
this is the distance a particle, subject to wave motion, is moved, from its mean position
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AMPLITUDE
the greatest displacement of any particle from its mean position (equilibrium)
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WAVELENGTH
the distance between two identical points on adjacent waves
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FREQUENCY
the number of cycles per second
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PERIOD
the time taken for one complete cycle
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THE VELOCITY OF A WAVE
is the distance traveled, by the wave front, per unit time
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DIFFRACTION
this is the process whereby a wave, exiting an aperture whose width is of the order of magnitude of the wavelength, spreads out, such that the direction of movement of energy is radically spread from the centre(s) of diffraction
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THE PRINCIPLE OF SUPERPOSITION
states that the total displacement at any point is the vector sum of the individual wave displacements for any waves interfering, at that point
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PHASE DIFFERENCE
this is the difference, in terms of position with the cycle of oscillation by which one vibration leads or lags another...
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INTERFERENCE
this is the phenomena whereby a particle is subject to oscillation from various waves and the principle of superposition applies
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COHERENCE
two sources are said t be coherent if they have constant phase difference (ie same frequency)
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PROGRESSIVE WAVE
a progressive wave is one which transfers energy from a source at the velocity of the wave
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STATIONARY WAVE
a stationary wave is said to exist within a closed system of source and reflector. there is no intended energy lost from this system
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NODES
these are that point on a stationary wave where there is no displacement at anytime. adjacent nodes are half a wavelength apart
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SNELL'S LAW
this states that for two particular media, the radio of the sine of the angle of incidence to the sine of the angle of refraction is constant
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REFRACTIVE INDEX OF SUBSTANCE
this is the speed of light in a vacuum divided by the speed of light in the substance
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TOTAL INTERNAL REFLECTION
this is the condition where a ray of light, travelling through a transparent medium, fails to exit that medium into an adjacent transparent medium but instead is reflected.
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CRITICAL ANGLE
if the angle of incidence is greater than the critical angle then the ray fails to exit the medium, but is instead reflected
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MULTI MODE (a)
this is the term used to describe fibres that are used for optical transmission that are so wide they allow a significant variety of paths of travel through them.
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MULTI MODE (b)
so much so that there is significant time difference in pulses that travel the 'shortest' route by comparison to that taken by those travelling the 'longest- zig zag' route
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STOPPING VOLTAGE
this is the electric potential energy equivalent to the kinetic energy of an electron, emitted from a metallic surface.
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THE ELECTRON VOLT
this is the energy change when an electron moves through a potential differnece of 1 Volt.
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THE WORK FUNCTION (of a material)
this is the minimum photon energy required to liberate an electron from a material
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THRESHOLD FREQUENCY
this is the minimum frequency of a photon that will just emit an electron from the associated metal upon which it is incident
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PHOTO-ELECTRON
this is the name some authors chose to give to electrons that have been emitted from a metal surface by the incidence of a photon
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LINE EMISSION SPECTRA
when this spectra is viewed though a diffraction grating, it forms a series of bright, uniquely coloured lines set against a dark background. each line is associated with a specific frquency/wavelength of EM emission
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LINE ABSORPTION SPECTRA
when this spectra is viewed through a diffraction grating, it forms a series of dark lines set against a bright, rainbow coloured background. each line is associated with a specific frequency/wavelength of EM absorption spectra
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EXCITATION OF AN ATOM
this is the process whereby atoms absorb energy without ionisation
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THE GROUND STATE
of an atom is that condition where rings of electrons are filled from the n=1 ring up, the atom is neutral
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STIMULATED EMISSION
the process by which an excited atom is caused, by the absorption of an incident photon, to re-emit the incident photon and additionally another photon. both photons will exit with the same frequency phase and direction
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POPULATION INVERSION
this is where the number of atoms in the excited state (N{2}) exceeds that number in the ground state (N{1})
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PUMPING
this is the process of feeding energy into the amplifying medium of a laser to produce a population inversion
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Other cards in this set

Card 2

Front

one amp of current is a coulomb of charge being moved, per second

AMPERE

Card 3

Front

the rate of flow of charge past a point

Card 4

Front

this states that for a metallic conductor at a constant temperature, the current flowing through it, is directly proportional to the P.D. across it

Card 5

Front

this is the P.D. placed across the device divided by the current flowing through it