Question

Red light (680nm) passes through a double slit and produces 17 birght fringes on a distant screen. How many bright frineges will be on the screen. if violet light 440 nm is used instead?

Answer 1

Lambda = 680 nm, 17 th Bright fringes y_17 We know that for bright Fringe y = n lambda D/d For red light y = (17) (680 nm) D/d - (i) For violet light y = n (440 nm) D/d implies (17) (680 nm) D/d = n (440 nm) D/d [from equation i] implies n = 17 times (680 nm)/(440 nm) = 26.27 Therefore 26 bright fringes will be on the screen