Longitudinal And Transverse Waves

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Longitudinal And Transverse Waves

  1. 1. Longitudinal and transverse waves
  2. 2. Longitudinal <ul><li>Sound </li></ul><ul><li>Seismic P-waves </li></ul><ul><li>Compression waves on string </li></ul><ul><li>Compressions </li></ul><ul><li>Rarefactions </li></ul>
  3. 3. Transverse <ul><li>Water waves </li></ul><ul><li>Waves on string </li></ul><ul><li>Seismic S-waves </li></ul><ul><li>EM waves </li></ul><ul><ul><ul><li>No vibrations of particles in a transmitting medium </li></ul></ul></ul><ul><ul><ul><li>Oscillating electric and magnetic fields </li></ul></ul></ul><ul><ul><ul><li>c = 3 x 10 8 ms -1 </li></ul></ul></ul>
  4. 5. Polarisation <ul><li>Evidence for transverse nature of waves </li></ul><ul><li>Using a Polaroid to view light </li></ul><ul><li>Using 2 Polaroids </li></ul>
  5. 6. <ul><li>Polaroid 1: only transmits waves in vertical plane </li></ul><ul><li>Polaroid 2: only transmits waves in horizontal plane  absorbs all waves in other planes </li></ul><ul><li>i.e. a polarised light detector </li></ul><ul><li>Longitudinal waves – cannot be polarised </li></ul>
  6. 7. Light <ul><li>Unpolarised </li></ul><ul><li>Plane polarised – oscillations restricted </li></ul><ul><li>EM radiation = varying E and B field </li></ul><ul><li> polarisation of plane containing E field </li></ul><ul><li>e.g. if light is vertically plane polarised, plane containing E field and direction of travel (plane of vibration) is vertical </li></ul>
  7. 8. Applications <ul><li>Sunglasses – reflected light partially plane polarised (sea/pond = horizontally plane polarised). Sunglasses only transmit vertically plane polarised light </li></ul>
  8. 9. <ul><li>Stress patterns – transparent polymers placed between crossed polarising filters </li></ul><ul><li>Camera lenses – polarising film can reduce light intensity (and increase contrast) since light from sky is partially plane polarised (light from cloud is not) </li></ul>
  9. 10. Polarising light <ul><li>Polarising filters </li></ul><ul><ul><li>transmitted light plane polarised parallel to filter </li></ul></ul><ul><li>Polaroid sheet </li></ul><ul><ul><li>Light absorbed if polarised parallel to molecular alignment </li></ul></ul>
  10. 11. <ul><li>Reflect it from transparent material </li></ul><ul><ul><li>Reflected ray – partially plane polarised parallel to surface (horizontal) </li></ul></ul><ul><ul><li>Refracted ray partially plane polarised perpendicular to surface (vertical) </li></ul></ul><ul><ul><li>If reflected ray perpendicular to refracted ray, both completely plane polarised (when angle incidence =  b Brewster’s angle) </li></ul></ul><ul><ul><li>Sunglasses – can check if polarising by looking at reflected light </li></ul></ul>
  11. 12. <ul><li>Scattering </li></ul><ul><ul><li>By suspension of small particles </li></ul></ul><ul><ul><li>Scattered light partially plane polarised </li></ul></ul><ul><ul><li>If scattered light at 90 ° to incident direction = completely plane polarised </li></ul></ul>

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