## EXPERT ANSWER

According to question, light has wavelength, = 646 nm = 646 * 10^{-9} m.

distance of screen from slits, D = 8.75 m

Distance between central bright fringe and second order bright fringe is, y = 5.16 cm = 5.16 * 10^{-2} m. i.e for n = 2

Since, for maxima

Where d is distance between slits and n is order of maxima

Therefore, on rearranging

—–equation 1

For minima, distance between central bright fringe and nth order minima (or dark fringe) is

putting all given values and calculated value(equation 1) in above equation we get

Therefore for n = 3

Therefore distance between the central bright fringe and third order minimum is 6.45 cm or 0.0645 m.