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 Φ=0.50D\Phi=0.50 \mathrm{D}. Newton's rings are observed in reflected light with wavelength λ=0.61μm.\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.

Reveal Answer
5.91. (a) r=2kλ(n−1)/Φ=3.5 mm,r=\sqrt{2 k \lambda(n-1) / \Phi}=3.5 \mathrm{~mm}, where k=10k=10; (b) r′=r^{\prime}= =r/n0=3.0 mm,=r / \sqrt{n_{0}}=3.0 \mathrm{~mm}, where n0n_{0} is the refractive index of water.
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