INTERFERENCE

  Thin-Film Interference •         When a light wave strikes the film, it is partially reflected (ray 1) and partially transmitted. •         The transmitted wave is partially reflected off the back surface (ray 2). •         This act of splitting each light wave into a matched pair of waves means that the reflected light from a thin film is coherent. •         The reflection of one color is enhanced when the two reflected waves are in phase for a given wavelength.    

  Wavelength of Light Young’s double-slit experiment can be used to find the wavelength of light. The  distance between the two slits  and between the  barrier and the screen  are kept constant. At points   P 1 P 1   and  P 2 P 2 , there are bright bands on both sides. But, the distance   ¯ ¯¯¯¯¯¯¯¯¯ ¯ S 2 P 1 S 2 P 1 ¯   is longer than  ​ ¯ ¯¯¯¯¯¯¯¯¯ ¯ S 1 P 1 S 1 P 1 ¯ ​ by a wavelength   λ �  which makes the two waves  in phase  at ​ P 1 P 1 ​. At point ​ P 0 P 0 ​, the phase angle between the two waves is zero. Therefore, a central bright band appears. Large Triangle The  angle theta  in this  right triangle  can be calculated using trigonometry. tan θ tan ⁡ � = x L Small Triangle The point  P 1 P 1  is located at the center of the first bright fringe. The path difference between the two wavefronts is: λ = ¯ ¯¯¯¯¯¯¯¯¯ ¯ S 2 P 1 − ¯ ¯¯¯¯¯¯¯¯¯ ¯ S 1 P 1 wavelength from double-s...