Waves

Waves

1. Wave motion

   • Transverse
     • Particles of the medium vibrate perpendicular to the direction of the waves velocity
     • Light
   • Longitudinal
     • Particles of the medium vibrate parallel to the direction of the waves velocity
     • Sound
     • Compression and rarefaction
   • Progressive
     • Waves that move through a material or a vacuum
       • Transfers energy from one place to another
   • Definitions
     • Displacement
       • The distance a point is from the normal/equilibrium
     • Amplitude
       • The maximum displacement of any point of a wave from it normal/equilibrium
     • Wavelength
       • The distance between 2 exactly similar points on a wave e.g. crest to crest
     • Period
       • The time taken for one complete oscillation of a point in a wave
     • Phase difference
       • The difference (cycle in degrees) between similar points on separate waves i.e how far out of step they are
     • Frequency
       • The number of oscillations per unit time of a point in a wave
         • F=1/T
     • Speed of a wave
       • V= f λ
     • Coherent
       • Waves with constant phase difference
   • Transfer of energy by particles that vibrate around a fixed point

2. Properties

   • Reflection
     • Depends of shape of surface and angle of incidence
       • Convex
         • reflected waves spread out
       • Concave
         • Reflected waves focus to one point
     • Wavelength the same
   • Refraction
     • Waves change speed and direction due to the medium they travel through
       • Wavelength decreased
       • Frequency remains constant
   • Diffraction
   • Polarisation
     • Can distinguish between longitudinal and transverse waves
     • When light passes through polaroid filters
       • Long-chain molecules absorb the oscillating waves
         • If the molecules are arranged vertically
           • Absorbs horizontal wave energy and allows vertical waves through
         • If the molecules are arranged horizontally
           • Absorbs vertical wave energy and allows horizontal waves through
         • Plane polarisation
     • Polarised vertically mean vertical component taken out & vice versa
     • Polarised sunglasses
       • Light is already partially polarised upon reflection
         • Reduces glare by selecting one polarisation of light waves
     • Malus's law
   • Interference
     • Superposition of waves
       • π Radians or 180 = zero resultant wave if same amplitude
       • π/2 or 90 =
       • 2π or 360 = combined amplitude

3. Electromagnetic waves

   • Radiation
     • Wavelength (m)
       • >10^6 to 10^-1
         • 10^-1 to 10^-3
           • 10^-3 to 7*10^-7
             • 7*10^-7 to 4*10^-7
               • 4*10^-7 to 10^-8
                 • 10^-8 to 10^-13
                   • 10^-10 to 10^-16
               • Red to violet
     • Radio
       • Micro
         • Infrared
           • Visible
             • UV
               • X-ray
                 • Gamma
   • Travel at same speed in a vacuum
   • UV
     • A
       • 400-320nm
       • Very penetrating and can cause wrinkles
     • B
       • 320-280nm
       • Produce vitamin D
       • Can damage DNA in skin cells and cause cancer
     • C
       • 280nm
       • Almost all absorbed by ozone layer
     • Sun cream
       • Titanium dioxide absorbs UV
   • Uses of each

4. Stationary waves

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