a beam of light consisting of two wavelengths 800nm and 600 nm is used to obtain the interference pattern in youngs double slit expt on a screen placed 1.4m away.if two slits are separated by 0.28mm,calculate the least distance from the central bright maximum where the bright fringes of the two wavelenghts coinside..? plz help

Answer 1

for the 600nm wavelength, then nth fringe occurs at

n*600*10^-9m * 1400mm/.28mm = n*.003m

for the 800 nm, it's n*.004m

So, the first coincidence is at .012m

This is discussed in an identical problem at

http://www.physicsforums.com/showthread.php?t=364763