Question

Diameter of $8^{th}$ dark ring in Newton's rings system viewed normally in reflected light of wavelength $5000 \mathring A$ is 4 mm. Radius of curvature of convex surface in contact with the glass plate is

• A. 1.5 m
• B. 1 m
• C. 0.5 m
• D. 2 m

Answer 1

Answer: (B)

1 m

Answer 2

Here, $\lambda = 5000 \mathring A , D_n = 4 \: mm$
As $D_n^2 = 4n \: R \lambda$
or $R = \frac{ D_n^2 }{4 n \lambda} = \frac{( 4 \times 10^{-3})^2}{4 \times 8 \times 5000 \times 10^{-10} } = 1 m$