cyeokpeng Posted November 16, 2004 Share Posted November 16, 2004 In a particular well-known experiment known as Newton's ring interference pattern, we get a dark fringe at the point of contact of the glass lens and the plane glass surface, followed by rings of bright fringes and dark fringes. This seems to show that at that point of contact, the monochromatic light reflected from the glass surface is 180 degrees out of phase with the light reflected from the lens surface. How can that be possible? Link to comment Share on other sites More sharing options...
swansont Posted November 16, 2004 Share Posted November 16, 2004 You get a bright fringe at the center. Link to comment Share on other sites More sharing options...
cyeokpeng Posted November 17, 2004 Author Share Posted November 17, 2004 From the physics of optics, as light is reflected to the angle near the normal incidence, it will suffer a 180 degrees phase change if the refractive index of the reflecting material is larger than that of the surrounding material. So, at the point of contact with the planoconvex lens and the plane surface, due to 180 degrees phase change, the two reflected waves should "destroy" each other. This should result in the centre point being dark followed by white bands, then dark lines. Any explanation for that? Link to comment Share on other sites More sharing options...
cyeokpeng Posted November 17, 2004 Author Share Posted November 17, 2004 From the physics of optics, as light is reflected to the angle near the normal incidence, it will suffer a 180 degrees phase change if the refractive index of the reflecting material is larger than that of the surrounding material. So, at the point of contact with the planoconvex lens and the plane surface, due to 180 degrees phase change, the two reflected waves should "destroy" each other. This should result in the centre point being dark followed by white bands, then dark lines. Any explanation for that? Link to comment Share on other sites More sharing options...
swansont Posted November 17, 2004 Share Posted November 17, 2004 There is no phase change, since the reflecting light is within the lens. It doesn't see a higher index material. Light reflecting off the plane is in air and does see a higher index, so that light undergoes a [math]\pi[/math] phase change. More Link to comment Share on other sites More sharing options...
swansont Posted November 17, 2004 Share Posted November 17, 2004 There is no phase change, since the reflecting light is within the lens. It doesn't see a higher index material. Light reflecting off the plane is in air and does see a higher index, so that light undergoes a [math]\pi[/math] phase change. More Link to comment Share on other sites More sharing options...
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