Waves 3

  • Created by: Hollie
  • Created on: 28-05-14 14:13
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  • Waves 3
    • Pulse-echo techniques
      • Used to detect the position and/or the motion of a boundary between two materials. A pulse is required to be reflected as an echo with time interval recorded
    • Doppler effect
      • When waves are emitted from a moving source or detected by a moving receiver, the detected frequency differs from the emitted. The shift in frequency is proportional to the relative speed of the motion
        • Shifts towards the red end show an object moving away and shifts towards the blue shows moving closer
      • Used in medicine: an ultrasound transducer is coupled to the body near an artery which emits a pulse that is reflected. A blockage or constriction can be detcted by a sudden change in the shift frequency
    • Ultrasound scanning
      • Reflected pulses of ultrasound are used to determine where the boundaries are between different tissues then an image is built up. The resolution can be improved by reducing the wavelength and using pulses of very short time intervals.
    • Polarisation
      • Unpolarised light -oscillations can be in all planes perpendicular to wave travel
        • Polarising filters - unpolarised light can enter a filter and become polarised, if polarised light enters then it depends on the orientation of the filter. Through two filters absorbs the light completely
      • Polarised light - oscillations are limited to one plane.
      • Transverse waves can be polarised yet longitudinal cannot
    • Diffraction
      • The change in direction of a wave as it passes through an obstacle e.g a narrow slit. The closer the gap is to the wavelength, the greater diffraction.
      • Evidence for wave nature of electrons
        • When a beam of electrons is directed at a crystal it is said the beam must have been diffracted through the layers of atom in the crystal, explaining a wave behavior. The wavelength of the beam must be similar to the distance.
  • The angle of incidence when the angle of refraction is 90 degrees. Greater than this, total internal reflection occurs


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