26.22. Set Up: The fringes are produced by interference between light reflected from the top and bottom surfaces of the air wedge. The refractive index of glass is greater than that of air, so the waves reflected from the top surface of the air wedge have no reflection phase shift and the waves reflected from the bottom surface of the air wedge do have a half-cycle reflection phase shift. The condition for constructive interference (bright fringes) is therefore The geometry of the air wedge is sketched in Figure 26.22. At a distance x from the point of contact of the two plates, the thickness of the air wedge is t . Figure 26.22 Solve: so and The distance along the plate between adjacent fringes is and The angle of the wedge is 26.23. Set Up: For the waves reflected at the top surface of the grease wedge, the waves are in material with refractive index 1.60 and reflect off material with refractive index 1.50. Therefore, there is no reflection phase shift. For the waves reflected at the bottom surface of the grease wedge, the waves are in material with refractive index
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