A double slilt experiment is performed with sodium (yellow) light of wavelength 589.3 nm and the interference pattern is observed on a screen 100 cm away. The tenth bright fringe has its centre at a distance of 12 mm from the central maximum. Find the separation betwen the slits.

Explanation

For the nth maximum fringe, the distance above the central line is
`x=(nlamdaD)/d`
According to the data given
`x=12mm, n=10, lamda=589.3nm, D=100cm.`
Thus the separation between the slits is
`d=(nlamdaD)/x=(10x589.3xx10^-9mxx100xx10^-2)/(12xx10^-3xxm)`
`=4.9xx10^-4m=0.49mm.`