# Definitions

 Acceleration rate of change of velocity with respect to time Ampere The current which when flowing in two straight parallel conductors of infinite length, placed one meter apart in a vacuum, would produce a force of 2×10-7 newtons per metre of length. Amplitude The distance top (or bottom) of a wave to the middle of the wave. Angular Speed/Velocity The rate of change of angle with respect to time Anode The positive electrode in a cell or solution. Atomic Number The number of protons in the nucleus. Becquerel SI unit for radioactive decay/activity, Becquerel(Bq) = 1 disintegration per second. Capacitance The ability of a material to store electric charge. Cathode The negative electrode in a cell or solution. Centre of curvature Centripetal acceleration The acceleration towards the centre of a body moving in a circle Centripetal force The force towards the centre needed to need a body moving in a circle. Chain reaction A self-sustaining nuclear reaction, the products of which need the reaction going. Coherent Light is coherent if the waves are in phase or have a constant phase relationship. Conductor A material capable of carrying an electric charge. Constructive interference Crests from one source always meet the crest from another source. Converging/convex lens Lens capable of bring to a point a beam of light passing through it. Coulomb SI unit of electric charge, 1 coulomb(C) = 1 ampere per second. Couple Two equal and opposite parallel, but not linear forces acting on a body. Critical angle The minimum angle of incidence at which total internal reflection occurs. Decay constant The probability of the decay of an atomic nucleus per second. Density Mass per unit volume Destruction interference Crests from one source always meet the trough from another source. Diffraction When the sideways spreading as a wave goes round obstacle or through a small gap. Diode A device that allows current to flow only in one direction. Dispersion The splitting of light into different wavelengths, creating a spectrum. Displacement A specified distance in a specified direction. (Vector) Diverging lens A lens that causes a parallel beam of light to diverge as it passes through. Doping Adding small amounts of impurity to a semiconductor to make it N or P type. Doppler effect The apparent change in frequency of sound or radiation due to the relative motion of the source and observer. Eddy currents Induced electric currents in conductors due to changing magnetic flux. Electric field strength The force per unit charge that a positive charge would experience if placed at that point in the field. Electromagnetic induction Whenever the magnetic field passing through a coil changes this causes an electromagnetic force in the coil. Electromotive Force The energy given to each coulomb of charge as it goes through a battery or generator. Farad SI unit of capacitance, 1F = 1 coulomb across potential difference of 1 volt. Focal Length The distance for the focal point to the mirror. Force Anything that causes the velocity of an object to change. Forward bias When a diode is connected to a battery so that current flows. Frequency The number of oscillation or cycles per second. Friction The force that opposes the sliding of surfaces in contact. Fundamental frequency The lowest possible vibration of a stationary wave. Half life The time taken for half of the undecayed atoms undergo a decay in a radioactive isotope. Harmonic A wave whose vibration is a whole multiple of the fundamental frequency. Heat Energy transfer from one place to another due to a temperature difference. Hertz Measure of frequency, 1 hertz is one cycle per second. Interference The addition or combination of waves, it can be either destructive or constructive. Isotope Atoms of that same element that have different mass numbers. They have different amounts of neutrons. Joule SI unit of Work or Energy, 1 joule = 1 newton metre Joule’s Law The heat power loss in a circuit is directly proportional to the square of the current flowing. Kinetic energy The energy a body possess by virtue of its motion. Lever A rigid body which is free to rotate about a fixed point. Longitudinal wave A wave whose direction of vibration is parallel to the direction the wave is travelling. Magnetic declination The angle between the magnetic North and true North at a point on the Earth’s surface. Magnetic dip The angle between the Earth’s magnetic field and the horizontal at a point on Earth. Magnetic Flux Density is the magnetic flux per unit area at right angles to the magnetic field. Mass number Number of protons and neutrons in the nucleus. Moment The force x perpendicular distance from the point to the line of action of the force. Momentum Mass x Velocity Mutual induction An emf is generated in a secondary coil due to a change in the magnetic field produced by the primary coil. Node A point of zero displacement in a standing wave. N-type semiconductor A type of semiconductor whose conductivity is caused by a flow of electrons. Nuclear Fission The Splitting up of a large nucleus into two smaller but similar sized nucleii. Nuclear Fusion The joining of two small nucleii to form a larger nucleus. Ohm The resistance of a conductor when a current of 1 amp flows in the conductor which has a potential difference of 1 volt across it. Ohm’s Law For a metal at constant temperature, voltage is equal to the current by the resistance. Pascal SI unit of pressure, 1 pascal = 1 newton per metre squared. Period The time a wave takes to travel one wavelength or for a object to make one orbit. Permittivity The measure of how a material can resist the flow of electric charge Phase Photoelectric effect The emission of electrons from the surface of a metal when electromagnetic radiation of suitable frequency falls on it. Photon A quantum of electromagetic radiation Pitch A measure of the frequency of a note. High pitch means high frequency. Plancks’s constant A constant relating the frequency of radiation to its quantum of energy. Potential difference/Voltage Between two points in an electric field is the work done in bringing a charge of +1 Coulomb from one point to the other. Potential energy The energy a body has due to its position. Power Rate at which work is done or the rate at which energy is converted from one form to another. Pressure The force per unit area acting on a surface. P-type semiconductor A type of semiconductor whose conductivity is caused by a flow of holes. Radioactivity The disintegration or decay of unstable nucleus with the emission of alpha, beta or gamma radiation. Real image An image formed by the actual intersection of rays and can be projected onto a screen. Refractive index The amount that light is bent when it goes from one medium to another. Resistance The potential difference between the ends of a conductor divided by current flowing through it. Resistivity The inverse of conductivity = RA/L where R is resistance, A is cross sectional area and L is the length. Reverse bias When a diode is connected to a battery so that no current flows. Root Mean Square (RMS) The square root of the average of the squares of current or voltage. Scalar quantity A quantity that depends only on magnitude. Self induction When an electromagnetic force is generated in a coil by a change in the magnetic field of the same coil. Semiconductor A material whose resistance is between an insulator and a conductor. Simple harmonic motion Specific heat capacity Of a substance is the amount of heat energy needed to change the temperature of one kilogram by one kelvin. Specific latent heat of fusion Of a substance is the amount of heat energy needed to change 1 Kg of that substance from a solid to a liquid. Specific latent heat of vapourisation Of a substance is the amount of heat energy needed to change 1 Kg of that substance from a liquid to a gas/vapour. Spectrum A band of colour produced when electromagnetic radiation are separated into different frequencies. Standing wave A wave formed when two identical (same frequency and amplitude) waves travelling in opposite directions meet. Temperature The measure of the hotness or coldness of a body. Tesla SI unit of magnetic flux density, 1 tesla = 1 weber per square metre. Thermionic emission The emission of electrons from a heated metal. Thermometric property A property of a body that changes with temperature. Thermistor Is a semiconductor device whose resistance decreases rapidly with increase in temperature. Threshold frequency The minimum frequency of the incident radiation for the photoelectric effect to take place. Total internal reflection The total reflection of light travelling cross for a medium to a medium of lower refractive index Triple point of water The unique temperature at which ice, water and vapour exist together (273.16K) Transverse wave A wave whose direction of vibration is perpendicular to the direction the wave is travelling. Vector quantity A quantity that depends on magnitude and direction Velocity The rate of displacement (speed) of a object in a given direction. Virtual image An image produced by the apparent intersection of rays. Volt SI unit of potential difference, 1 volt = 1 joule per coulomb. Watt SI unit for Power, 1 watt = 1 Joule per second. Wavelength The distance between two successive crests. Weber (Wb) SI unit for magnetic flux, 1 weber = 1 Tesla metre squared. Weight The force of attraction of the earth on a given mass. Work Force x Distance Work function The minimum energy needed to release an electron from a metals surface.
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