NEET-XII-Physics
17: Light Waves
- #40Light 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?Ans : Given:
Wavelength of the light used, `` \,\mathrm{\,\lambda \,}=560\,\mathrm{\,nm\,}=560\times {10}^{-9}\,\mathrm{\,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}\,\mathrm{\,m\,}\,\mathrm{\,or\,}=0.683\,\mathrm{\,cm\,}``
Hence, the diameter 2R of the central bright spot on the wall is 1.37 cm.
Page No 383: