All Problems Interference of Light
Problem 5.91
Two thin symmetric glass lenses, one biconvex and the other biconcave, are brought. into contact to make a system with optical power \(\Phi=0.50 \mathrm{D}\). Newton's rings are observed in reflected light with wavelength \(\lambda=0.61 \mu \mathrm{m} .\) Determine: (a) the radius of the tenth dark ring; (b) how the radius of that ring will change when the space between the lenses is filled up with water.
5.91. (a) \(r=\sqrt{2 k \lambda(n-1) / \Phi}=3.5 \mathrm{~mm},\) where \(k=10\); (b) \(r^{\prime}=\) \(=r / \sqrt{n_{0}}=3.0 \mathrm{~mm},\) where \(n_{0}\) is the refractive index of water.