Question

Abeam of light consisting of two wavelengths, 650 nm and 520 nm, isused to obtain interference fringes in a Young’s double-slitexperiment.

(a) Findthe distance of the third bright fringe on the screen from thecentral maximum for wavelength 650 nm.

(b) Whatis the least distance from the central maximum where the brightfringes due to both the wavelengths coincide?

Answer 1

Wavelength of the lightbeam,

Wavelength of anotherlight beam,

Distance of the slitsfrom the screen = D

Distance between thetwo slits = d

(a) Distance of the n^th bright fringe on thescreen from the central maximum is given by the relation,

(b) Let the n^th bright fringe due towavelength and(n − 1)^th bright fringe due to wavelength coincide on the screen. We can equate the conditions for brightfringes as:

Hence,the least distance from the central maximum can be obtained by therelation:

Note:The value of d and D are not given in the question.