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G482 - Electrons, Waves and Photons Definition List COULOMB The charge transported by a steady current of one ampere in one second ELECTRIC CURRENT CONVENTIONAL The flow of charged particles Direction in which positive charges would flow in a circuit CURRENT RESISTANCE Potential Difference / Current RESISTIVITY Resistivity = R A / L, where R is the resistance of the material, A is the cross-sectional area of the material and L is the length of the material OHM's LAW For a metallic conductor at constant temperature, the current in the conductor is directly proportional to the potential difference across its ends. KIRCHHOFF'S The sum of the currents entering a point is equal to the sum of the FIRST LAW currents leaving the same point KIRCHHOFF'S The sum of the e.m.f.'s around any closed loop in a circuit is equal SECOND LAW to the sum of the p.d.'s around the same closed loop MEAN DRIFT The average distance travelled by the electrons along the wire per VELOCITY second KILOWATT-HOUR The energy transformed by a 1 kW device in a time of 1 hour POTENTIAL The energy transferred (lost) per unit charge DIFFERENCE ELECTROMOTIVE The energy transferred (gained) per unit charge FORCE PROGRESSIVE A transfer of energy as a result of the oscillations of the WAVE medium or particles through which the energy is travelling LONGITUDINAL Wave vibrations are parallel to the wave direction WAVE TRANSVERSE Wave vibrations are perpendicular to the wave direction WAVE DISPLACEMENT The distance of a point on the wave from the equilibrium (WAVES) position AMPLITUDE The maximum displacement of any point on the wave from the (WAVES) equilibrium position WAVELENGTH The distance from any point on the wave to the next (WAVES) subsequent point in phase WAVE SPEED The speed at which energy is transmitted by the wave (WAVES) FREQUENCY The number of oscillations at a point per unit time (WAVES) PERIOD The time taken for one complete oscillation (WAVES) INFRARED RADIATION Part of the EM spectrum with a wavelength of 1 x 10-6 m INTERFERENCE When two waves meet at a point, there is a change in the overall displacement PRINCIPLE OF When two waves interfere at a point, the resultant displacement SUPERPOSITION is the sum of the individual displacements PATH The extra distance travelled by one of the waves compared with the DIFFERENCE other COHERENCE A constant phase difference between the waves COHERENT Sources of waves which have a constant phase difference SOURCES DIFFRACTION The spreading out of a wave after passing through a gap or around an obstacle PLANE Plane polarised waves oscillate in one plane only POLARISATION INTENSITY The rate of energy transmitted per unit area at right angles to the direction of propagation (W/m2) STANDING A wave consisting of nodes and antinodes which does not transfer energy WAVE NODE A point where the amplitude of vibrations is always zero ANTINODE A point where the amplitude of vibrations takes the maximum possible value THRESHOLD The minimum frequency of radiation needed for electrons to be FREQUENCY ejected from a metal surface PHOTON A packet of energy OR a quantum of electromagnetic radiation ELECTRONVOLT The energy gained by an electron which is accelerated through a potential difference of 1 volt WORKFUNCTION The minimum energy required to eject an electron from a metal OF A METAL surface CONTINUOUS All wavelengths are present in the radiation SPECTRUM