Question

In a Youngs double-slit experiment, the slits are separated by 0.28 mm and the screen is placed 1.4 m away. The distance between the central bright fringe and the fourth bright fringe is measured to be 1.2 cm. Determine the wavelength of light used in the experiment.

Answer 1

Distance between the slits, $d=0.28\times {10}^{-3}m$

Distance between the slits and the screen, $D=1.4m$

Distance between the central fringe and the fourth $(n=4)$ fringe,

$u=1.2\times {10}^{-2}m$

In case of a constructive interference, we have the relation for the distance between the two fringes as:

$u=n\lambda D/d$

$\Rightarrow \lambda =ud/nD=6\times {10}^{-7}m=600nm$