current whose magnitude and polarity are constantly changing - alternating current, current whose polarity remains constant - direct current, the ratio sinθ1/sinθ2 where θ1 is in a vacuum, and θ2 is in the medium - absolute refractive index, the number of protons in an atomic nucleus - atomic number, Doppler-shifting of a light wave towards the shorter wavelength end of the spectrum - blueshift, Doppler-shifting of a light wave towards the shorter wavelength end of the spectrum - redshift, the ratio of electric charge to potential difference between any two conductors separated by an insulating material - capacitance, waves that have the same frequency, speed and have a constant phase relationship - coherent waves, two vectors which act at right angles, the vector sum of which is the original vector - components of a vector, when two or more objects interact, the total momentum is conserved, in the absence of external forces - conservation of momentum, the maximum value of the angle between the normal and the ray in glass, θglass, for which refraction can occur - critical angle, theoretical form of energy accounting for most of the energy in the universe and causing its expansion to accelerate - dark energy, type of matter which does not interact with electromagnetic radiation so is invisible to astronomers - dark matter, area surrounding the p-n junction of a diode where the electrons have combined with the holes leaving no free charges - depletion layer, effect that causes waves to bend as they go past the end of an obstacle or through a small gap in a barrier - diffraction, a specified distance from a fixed point, in a specified direction. A vector quantity - displacement, observed change in frequency of a wave caused by relative motion between the source and observer - Doppler effect, collision in which both momentum and kinetic energy are conserved - elastic collision, flow of charged particles - current, electrical potential energy that is given to each unit of charge that passes through the source - electromotive force, any atomic energy level higher than the ground state - excited state, splitting of a large atomic nucleus into smaller fragments, with the resultant release of excess energy - fission, diode connected in a circuit such that the p-type terminal is more positive than the n-type terminal - forward biased, number of complete cycles of a wave passing a given point in a given time - frequency, the force acting per unit mass placed at a point in the field - gravitational field strength, the change of momentum of an object - impulse, the deliberate splitting of a large nucleus caused by the collision of the nucleus with a neutron - induced fission, collision in which momentum is conserved but kinetic energy is not - inelastic collision, opposition to current in a source of electrical energy - internal resistance, power per unit area of radiation incident on a surface - irradiance, different forms of the same element containing the same number of protons but different numbers of neutrons - isotopes, a spectrum that consists of narrow dark lines across an otherwise continuous spectrum - line absorption spectrum, a spectrum consisting of narrow lines of light, the position of which depend on the substances producing the light - line emission spectrum, the potential difference that is used to drive a current through the internal resistance of a source - lost volts, the total number of nucleons in the nucleus of an atom - mass number, the product of the mass of an object and its velocity - momentum, the force that, when applied to an object of mass 1 kg, will cause the object to accelerate at a rate of 1 ms-2 in the direction of the applied force - newton, semiconductor material that has an excess of free electrons - N-type semiconductor, a line drawn at right angles to a surface or the boundary between two different media - normal, the current in a conductor at constant temperature is directly proportional to the potential difference across it - Ohm's Law, a circuit in which the current is zero. In the circuit there is a gap or an infinite resistance - open circuit, the difference in path lengths of two sets of waves - path difference, the time to make one complete wave - period, a type of p-n junction diode that responds to light intensity - photodiode, the emission of electrons from a metal due to the effect of electromagnetic radiation - photoelectric effect, the emission of electrons from a material caused by light shining on it - photoemission, the mode of operation of a photodiode where it can supply power to a load. This is the basis of a solar cell. - photovoltaic mode, a source of radiation with equal irradiance in all directions regarded as so small within its frame of reference as being equivalent to as single point - point source, a measure of the work done in moving one coulomb of charge between the two points - potential difference, a circuit consisting of a number of resistors (often only two) in series, connected across a supply, that is used as a source of fixed or of variable p.d - potential divider, an object that is flying through the air under the influence of gravity - projectile, semiconductor material that has an excess of free holes - P-type semiconductor, the ratio of potential difference across the conductor to the current through it - resistance, when a wave goes from one medium into another - its speed and wavelength always change; its frequency never changes; its direction sometimes changes - refraction, a diode connected in a circuit such that the p-type terminal is more negative than the n-type terminal - reverse biased, a physical quantity which has magnitude but no direction - scalar, a circuit in which the current is at its maximum. In this type of circuit the resistance connected across the terminals of the source is 0 Ω - short circuit, the potential difference that appears across the terminals of a source when the source is supplying a current to a circuit - terminal potential difference, the minimum frequency of electromagnetic radiation that will cause photoemission for a particular substance - threshold frequency, a physical quantity which has direction as well as magnitude - vector, the rate of change of displacement - velocity, the gravitational force acting on a mass - weight, the minimum energy required to cause photoemission from a particular substance - work function, the rate of change of velocity - acceleration,

H Physics glossary - definitions flashcards

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