Newton's Rings and plano-convez lens

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The discussion focuses on a plano-convex lens resting on a flat glass surface, illuminated by light of wavelength 521 nm, resulting in a central dark spot and 15 concentric dark rings. The question posed is about calculating the thickness of the air wedge at the position of the 16th dark ring compared to the center. The proposed solution indicates that the thickness difference is 3.90 X 10^-7 m, derived by multiplying the wavelength by 15 and dividing by 2. Participants suggest that this problem involves interference and reference a formula related to Newton's rings. The discussion emphasizes the need for a proper understanding of the underlying equations for accurate calculations.
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Homework Statement


A plano-convez lens (flat on one side, convez on the other) rests with its curved side on a flat glass surface. The lens is illuminated from above by light of wavelength 521 nm. A dark spot is observed at the centre, surrounded by 15 concentric dark rings (with bright rings in between). How much thicker is the air wedge at the position of the 16th dark ring than at the centre?


Homework Equations


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The Attempt at a Solution


The answer says 3.90 X 10^-7m. By multiplying the wavelength by 15 and then dividing it by 2, i get this answer.. by why? Is there actually an equation for these type of problems?
 
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