WAVES

WAVES

1. Parts of a wave

   • CYCLE - One complete vibration of a wave
   • AMPLITUDE - Maximum magnitude of displacement
   • WAVELENGTH - Length of one whole wave cycle, from crest to crest or trough to trough
   • PERIOD - Time taken for whole cycle to complete
   • FREQUENCY - Number of cycles per second passing a given point
   • PHASE - Measure of position of certain point along wave cycle
     • PHASE DIFFERENCE - Amount one wave lags behind another

2. Types of wave

   • Longitudinal
     • Vibrate in same direction as energy transfer
   • Transverse
     • Vibrates perpendicular to the direction of energy transfer

3. Polarisation

   • Only transverse waves can be polarised
   • Examples
     • POLAROID SUNGLASSES - Block out unwanted glare
     • TV SIGNALS - Polarised by orientation of rod on broadcasting aerial
   • Ordinary light can be polarised using polarising filter
     • Two polarising filters at right angles to each other will let no light through

4. Interference

   • Node formed from destructive interference
     • Destructive = Crest + Trough
   • Antinode formed from constructive interference
     • Constructive = crest + crest / Trough + trough
   • Stationary wave formed when 2 progressive waves travel with equal and opposite velocities and have the same frequency/ wavelength and same amplitude.
   • COHERENT SOURCES - constant phase difference, same wavelength and similar amplitudes

5. Diffraction

   • Single Slit
     • Central maximum is brightest part
     • INCREASING SLIT WIDTH - decreases the amount of diffraction, the central maximum is narrower and has higher intensity
     • INCREASING WAVELENGTH - increases amount of diffraction, central maximum is wider and intensity is lower
   • Young's double slit
     • Destructive interference = Dark fringes
     • Constructive interference = Bright fringes

6. Refraction

   • When light travels from one median to another it bends
     • From air to glass - bends towards the normal
     • From glass to air - bends away from the normal
     • Light bends because speed of light and wavelength changes as it passes a boundary
   • REFRACTIVE INDEX - Measure of how much a substance bends light by changing its speed
     • The bigger the refractive index the more light is slowed and refracted