Question

Light of wavelength 560 nm goes through a pinhole of diameter 0.20 mm and  falls on a wall at a distance of 2.00 m. What will be the radius of the central bright spot formed on the wall?

Answer 1

Given:-

Wavelength of the light used,

\[\lambda = 560 nm = 560 \times {10}^{- 9} m\]

Diameter of the pinhole, d = 0.20 mm = 2 × 10⁻⁴ m

Distance of the wall, D = 2m

We know that the radius of the central bright spot is given by

\[R = 1 . 22\frac{\lambda D}{d}\]

\[       = 1 . 22 \times \frac{560 \times {10}^{- 9} \times 2}{2 \times {10}^{- 4}}\]

\[       = 6 . 832 \times  {10}^{- 3} m\text{ or }= 0 . 683  cm\]

Hence, the diameter 2R of the central bright spot on the wall is 1.37 cm.