Question

Two straight and narrow parallel slits 0.8 mm apart are illuminated using a monochromatic light source. A screen placed at a distance of 100 cm is used to obtain fringes. It is found that the distance between consecutive fringes is 0.5 mm. Determine the wavelength of light.

Answer 1

$$\begin{gathered} \beta =\frac{\lambda D}{d} \\ \lambda =\frac{\beta d}{D}=\frac{0.5\times {10}^{-3}\times 0.8\times {10}^{-3}}{100\times {10}^{-2}}=40\times {10}^{-8}m \end{gathered}$$