Waves yr 1

Waves yr 1

1. all electromagnetic waves are transverse

   • transverse waves; waves with direction of vibrations perpendicular to the direction of propagation of the wave.
     • longitudinal wave; waves travel with direction of vibrations parallel to the direction of propagation of the wave
       • sound
     • all transverse wave have a speed of c
   • red light- 780 nm
   • blue light-450nm

2. wave properties

   • reflection
     • when a wave hits a surface then bounces/reflects back
   • diffraction
     • when waves move through a gap and wave spreads out. the similar the wavelength of the wave and the distance of the gap, the larger the diffraction. more separation is wavelength is made larger or gap made narrower
   • refraction
     • when a wave changes direction when it enters a different medium
     • incident ray, the ray of light that comes in. touches the normal at the angle of incident. the refracted ray is the bended ray coming out which touches the normal at the angle of refraction
       • sin r proportional to sin i
         • sin i/sin r = n (constant=REFRACTIVE INDEX)= Snells law
           • n= speed in air/speed in glass
             • sin c=n air/n glass
               • if critical angle is bigger than sin c if critical angle then TIR occurs
                 • Total internal reflection
                   • modal dispersion
                     • to overcome can have a narrower inner core so less space for the light to disperse (in monomode optical fiber) can apply filter
   • poliarisation
     • only applicable to transverse waves e.g light so that wave travels in one plane only

3. intensity is the amount of energy per sec per sqr metre

   • intensity = power/ area
     • intensity is proportional to Amplitude^2

4. consructive/destructive interference

5. coherence- when 2 wave sources emit waves with constant phase difference

   • must be same wavelength hence same colour, monochromatic
   • path difference, measured in metres of fractions of wavelengths
     • n lambda: constructive interference
       • n/2 lambda: destructive interference
   • phase difference, measured in degrees or radians

6. youngs double slit experiment -when using monochromatic light

   • bright fringes formed when waves from each screen arrives in phase with each other
     • dark fringes formed when waves from each slit is 180 deg out of phase to each other
       • fringe separation is greater for red light than blue light because red light has a larger wavelength than blue light
   • double slit equation, w= fringe separation, lambda = wavelength of light, D= distance from the slit to the screen, s= slit spacing
   • youngs double slit exp when using white light
     • get a colourful spectrum
       • central colour is white as every colour contributes to the center of the pattern. inner sides are tinged with blue and blue on the outer side
         • this is because red light is more spaced out than blue light and the two fringe patterns dont overlap exactly
           • outer fringes merge into white light and become fainter with increasing distance from the centre. This is because the different coloured fringes overlap and create white light
   • waves must be at same frequency

7. single slit exp

   • dark and light fringes. most intense fringe at the centre
     • the centre fringe is twice as wide as the outer fringes
       • peak intensity decreases with distance from the centre
         • each of the outer fringes are the same width
           • the WIDTH of the central fringe= wavelenght of light/width of single slit * 2*Distance from the slit to the screen
             • therefore fringes are narrower using blue light rather than red light

8. diffraction grating

   • d sin feta= n lambda
     • sin feta proportional to lambda
       • blue colour closest to the white light smaller wavelenght so spreads out less
         • number of slits per metre N = 1/d (spacing grating)
           • sin90=1
             • n=d/lamba

9. types of spectra

   • continuos spectra
   • line emission
     • emits light at specific wavelenghts
   • absorption spectrum
     • dark lines are the light abrorbed

10. mass/lenght= muon

    • velocity (of wave) = *sqr rt* Tension/ muon

11. standing/stationary waves

    • distance from node to node is = half wavelenght
    • energy is stored
    • no displacement at the node, maximum displacement at the antinode
    • first standing wave=fundamental, Length= half a wavelength therefore wavelength = 2L this happens at a certain frequency called f0
      • second harmonic, wavelnght= L, has 2f0
        • third harmonic, wavelnght =2/3 L, has 3f0
          • fourth harmonic, wavelength l/2, has 4f0

12. progressive waves transfer energy

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