Monochromatic light falling on two slits 0.042 mm apart produces the fifth order fringe at a 7.8o angle. What is the wavelength of the light used?
The fringes are the constructive interference which occurs at
nl = dsinq
Where n is the order, in this case, 5, so we have:
5l = dsinq
l = dsinq/5
l = (.042E-3 m)(sin(7.8o)/5) = 1.1x10-6 m = 1.1 mm