Waves

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  • Created by: Pops!
  • Created on: 07-02-17 11:37

Wave Motion

  • Oscillations can produce waves, which carry energy
    • Energy ccarried in a wave depends on its amplitude 
    • Energy is directly proportional to amplitude squared
  • Frecuency is related to the period  f=1/T
  • Wavelength, frequency and speed of wave are related  v=f
  • Phase difference gives difference between similar points on two waves - measured in degrees/radians
  • TRANSVERSE - oscillations at right angles to direction in which wave is moving
    • Can be polarised (by removing all components exept those in plane of oscillation)
  • LONGITUDINAL - oscillations in same direction that wave is moving
    • Can't be polarised
  • As a wave spreads out, its intensity decreases by an inverse-square law I=P/4r2
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Reflection & Refraction

  • Angle of incidence = angle of refraction   i=r
  • n = refactive index  n=sini/sinr
  • refractive index of a medium = speed of light in a vacuum/speed of light in the medium
  • n1sin(http://2.bp.blogspot.com/-YScodKxEk-Q/UaDA0EoSC_I/AAAAAAAABGQ/5LmpsS5TyJ0/s1600/400px-greek_lc_theta-svg.png)1 = n2sin(http://2.bp.blogspot.com/-YScodKxEk-Q/UaDA0EoSC_I/AAAAAAAABGQ/5LmpsS5TyJ0/s1600/400px-greek_lc_theta-svg.png)2   when light moves from one medium to another
  • n=1/sinc   c = critical angle
  • If the angle of incidence in an opticaly more dense medium is greater than the critical angle TOTAL INTERNAL REFLECTION takes place
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Interference

  • Principle of superposition = when 2 or more waves meet, the resultant displacement is found by adding the displacements together
  • Waves interfere constructively IN PHASE
  • Waves interfere destrucively in ANTIPHASE
  • When waves reflect forwards and backwards, they superimpose and form a stationary wave
    • Stationary waves have nodes and anti-nodes (distance between adjacent nodes = 1/2)
    • Stationary waves have certain definite frequencies at which it will resonate
  • First harmonic of stretched wire -  (http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/imgwav/vibstr4.gif)
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Diffraction

  • When waves pass through a gap, they diffract - narrow gaps cause more spreading
  • Young's double slit experiment has 2 slits at distance s apart, which give a pattern of maxima and minima viewed from a distance of D away
  • The separation between adjacent maxima = w  so...  (http://physicsnet.co.uk/wp-content/uploads/2010/08/youngs-double-slit.jpg)
  • A diffraction grating gives a sharper, brighter maxima than Young's experiment
  • The diffraction grating equation is: (http://physicsnet.co.uk/wp-content/uploads/2010/08/diffraction-grating-equation.jpg) for the nth-order maximum
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