Light with λ = 420 nm in incident normally onto the flat side of a plano-convex lens which is resting on a glass plate parallel to the flat side of the lens and forms a pattern of concentric luminous and dark rings (Newton's rings). The radius of the second dark ring is 2.0 mm. What is the radius of curvature of the curved side of the lens?
A)9.6 m
B)2.4 m
C)4.8 m
D)7.2 m
E)1.2 m

Question

Quizplus · Accepted Answer

The radius of curvature R can be found using the formula for Newton's rings: $ R = \frac{r^2}{m \cdot \lambda} $, where r is the radius of the m-th dark ring, m is the ring number, and λ is the wavelength. For the second dark ring (m=2), $ R = \frac{(2.0 \times 10^{-3})^2}{2 \times 420 \times 10^{-9}} = 4.8 \, \text{m} $.

Light with λ = 420 Nm in Incident Normally onto the Flat