# Waves

• 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
• n1sin1 = n2sin2   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 -
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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...
• A diffraction grating gives a sharper, brighter maxima than Young's experiment
• The diffraction grating equation is:  for the nth-order maximum
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