Optics and Diffraction AS Physics

Optics and Diffraction AS Physics

1. Diffraction

   • Diffraction happens when a wave hits an obstacle or gap, the waves bend round the object or spread out when they pass through the gap, this is called diffraction.
   • Diffraction is greatest when the gap is about the same size as the wavelength of the wave.
   • Single Slit Diffraction
     • When monochromatic laser light is shone through a narrow single slit a diffraction pattern is produced consisting of light and dark fringes. It produces a wide central bright fringe. The other bright fringes get dimmer as you move away from the centre.
   • Diffraction Grating
     • A diffraction grating is a piece of glass with lots of closely spaced parallel lines on it each of which allows light to pass through it, this is a transmission diffraction grating.
       • d=1/N where N is the number of lines per metre on a diffraction grating

2. Interference

   • Coherence – two waves are coherent if the phase difference between them is constant. For this to be the case they must have the same frequency
   • Monochromatic – means having only one wavelength of light present.
   • Young's Double Slit Experiment
     • When laser light passes through a slit it is diffracted. If there are two slits present the light will diffract at both slits.
       • If a screen is placed on the other side of the slits from the laser an interference pattern is seen. It produces a series of bright and dark fringes.
     • w=fringe spacing
       • D = distance between the double slits and the screen
         • s = slit separation

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