Light and Matter

Light and Matter

1. Wave Models

   • Key Terms
     • Wavelength (Lamda)
       • 1 Wavelength = 1 Period
       • Wavelength shortens in water
     • Frequency (Hz)
       • Waves per second
     • Time of wavelength = time period (s)
     • v = fλ
     • Progressive/Travelling waves
       • Waves which transport
     • Types of Waves
       • Longitudinal
         • Mainly sound
       • Transverse
         • Mainly light
   • Wave Behaviours
     • Reflection
       • Light reflects at same angle
     • Refraction
       • Changes v when hits another material
         • Can get change in direction
     • Diffraction
       • The spreading out of a wave as it goes through a small gap
         • This will ALWAYS happen
       • Degree of diffraction depends on relative size of gap compared to wavelength
         • Small gap + Large wave = lots of diffraction
         • Large gap + small wave = little diffraction
         • If wavelength > or = gap then you get complete diffraction
           • Complete diffraction is λ/w >or= 1
             • Complete diffraction has a shadow
       • Can also occur to get around obstacles
         • Size of shadow region reduces as λ/diameter ratio increases
           • Max diffraction taken as λ/diameter >or= 1
           • More diffraction = less shadow
             • There is always a shadow though
       • Less diffraction in water
   • Light is an electro magnetic wave

2. The light spectrum

3. Interference and Young's double slit

   • Supports Wave Model
   • Interference
     • Can only happen with waves
     • Two types
       • Constructive
         • antinodes
       • Destructive
         • nodes
     • Waves continue on after interference
   • Troughs and crests
     • Troughs are lines
     • Crests are the dark
     • Crest meets crest and trough meets trough
       • Constructive interference
         • pd = nλ (a WHOLE NUMBER of wavelengths)
         • Must be a bright region
     • Crest meets trough
       • Destructive interference
         • pd = (n-(1/2))λ
   • Central maximum pd = 0
     • Always constructive
   • y = λD/a
     • Separation between pattern bands (y)
     • Distance to screen from slits (D)
     • Distance between two slits (a)

4. The Photoelectric Effect

   • Electron-Volts (eV)
     • 1eV = 1.6x10^-19J

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