Waves Section 1

Waves Section 1

1. Longitudinial Waves

   • Rarefactions and Compressions
   • Parallel to the direction of travel
   • Sound waves

2. Transverse Waves

   • Polarisation
     • The direction in which the particles vibrate in the plane perpendicular to travel
     • Polaroid glasses reduce the light intensity from Sun
     • 2 Polaroids orientated at 90* let no light go through
     • Longitudinial waves cannot be polarised
     • Polaroid allows light to pass where waves oscillates in 1 orientation
     • Used in aerials, need same orientation to get maximum signal, if rotated by 90* no signal received
   • Perpendicular to direction of travel
   • Light waves

3. Refraction

   • Occurs when a wave crosses a boundary where the speed changes
   • Arriving at surface = Leaving surface
   • Increasing wave speed = direction of wave must bend away from normal
   • Decreasing wave speed = direction of wave must bend towards normal
   • Sometimes partially transmit and reflect
   • The waves across a boundary must be continuous - same amount of wave fronts arriving
   • Light transmits through glass as well as reflecting it
   • Snell's Law
     • Relationship between incident and refracted angle is a function of the speeds the waves travel through the material

4. Total Internal Reflection

   • Incident Angle is greater than the Critical Angle
   • Light therefore reflects at the boundary
   • T.I.R is used in optic fibres, which has a core and cladding either side
   • Light shone into the core at greater angle to make sure it reflects
   • Core needs to be narrow - cut down on multi-mode dispersion - result in light travelling at different times
   • Optic Fibres
     • Cladding allows the signals to be transported seperately
     • In Optic Fibres if the light is wrong angle it can refract through the cladding
     • With no boundary the signals will become mixed up and interfere each other

5. Phase Difference

   • Tells us point of disturbance in cycle

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