3 Plane waves from a magnesium lamp 2 518 36 nm arrive

Last updated: 6/7/2023

3 Plane waves from a magnesium lamp 2 518 36 nm arrive perpendicularly on an opaque screen containing a long 0 250 mm wide slit A large nearby positive lens forms a sharp image of the Fraunhofer diffraction pattern on a screen The center of the fourth dark fringe is found be 1 20 mm from the central axis Determine the focal length of the lens