AS 2 Physics definitions

• Transverse wave


  The displacement which produces the wave is perpendicular to the direction in which the wave travels
• Longitudinal wave


  The displacement which produces the wave is parallel to the direction in which the wave travels
• Amplitude


  The maximum displacement of the wave from its equilibrium position
• Frequency


  The number of complete waves that pass a point in one second
• Frequency


  The number of oscillations occurring in one second
• Time period


  The time it takes for an oscillation or wave to complete one full cycle
• Wavelength


  The distance from any point on a wave to a corresponding point on the next wave
• Phase difference


  How much a particle is in front of or behind another particle, expressed as a fraction of one cycle
• Unpolarised wave


  One in which the vibrations occur in more than one plane
• Polarised wave


  One in which the vibrations occur in a single plane
• Snell's Law


  The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for light traveling from one medium to another
• Critical angle


  The angle of incidence, for light traveling from one medium to a less optically dense medium, which results in an angle of refraction of 90°
• Axial mode


  The path along the fiber's central axis
• Higher-order mode


  The path made up of repeated total internal reflections at just above the critical angle
• Coherent fibers


  Fibers arranged to run parallel to each other
• Incoherent fibers


  Fibers that all run from one end to the other but are not carefully aligned
• Focal point


  The point through which rays parallel to the principal axis that pass through the lens are refracted, converge to an appear to diverge from
• Magnification


  The ratio of image height to object height
• Myopia


  Short-sightedness - results in a person being unable to see distant objects sharply
• Hypermetropia


  Long-sightedness - results in a person being unable to see near objects sharply
• Power of a lens

  The reciprocal of the focal length of a lens when the focal length is in metres
• Principle of superposition


  When two or more waves meet, the resultant displacement of the medium is the vector sum of the displacements that each wave would cause at that point
• Standing wave


  A stationary pattern of peaks and troughs produced by the superposition of two waves of the same wavelength, frequency and speed moving in opposite directions
• Interference pattern


  The pattern obtained when two or more waves superimpose to produce distinct regions of constructive interference and destructive interference
• Diffraction


  The spreading out of waves when they pass through a gap or meet an obstacle
• Diffraction patterns with light

  The pattern of maxima and minima obtained as a result of interference of light waves as they diffract on passing through one or more narrow slits
• Photoelectric effect


  The effect in which electrons are emitted from a metal when electromagnetic radiation of sufficiently high frequency falls onto it
• Photon model of light


  EM radiation is regarded as discrete packets or quanta of EM energy called photons. The energy of a photon depends on its frequency
• Electron volt


  A unit of energy equivalent to the amount of energy an electron gains when it is accelerated across a potential difference of one volt
• Energy levels in an atom


  Specific sets of orbits of fixed size and energy in which electrons can exist. Electrons can move from one energy level to another but cannot exist between levels
• LASER action


  Light Amplification by Stimulated Emission of Radiation
• Production of X-rays


  The bombardment of a metal target with high-speed electrons resulting in the movement of electrons between energy levels inside the atoms of the target and the emission of high-energy photons (X-rays)
• Wave-particle duality


  The concept that waves can be considered as both waves and particles; whilst, particles can be shown to exhibit both particle and wave-like properties
• Doppler shift


  The change in the observed frequency and wavelength of a wave emitted from a source which is itself moving relative to the observer
• Hubble's Law


  The recessional velocity of a galaxy is directly proportional to its distance from the Earth
• Coherent light


  Light of a constant phase difference