Question

In a Young's double-slit experimental set-up with slit separation \(0.6\ \text{mm}\), a beam of light consisting of two wavelengths \(440\ \text{nm}\) and \(660\ \text{nm}\) is used to obtain an interference pattern on a screen kept \(1.5\ \text{m}\) in front of the slits. Find the least distance of the point from the central maximum where the bright fringes due to both the wavelengths coincide.

Hint:

For coincidence of bright fringes in YDSE, always use \[ n_1\lambda_1=n_2\lambda_2. \] First find the smallest integral values of \(n_1\) and \(n_2\), and then substitute into \[ y=\frac{nD\lambda}{d} \] to determine the position of the coincident bright fringe.

Answer 1