Question

in young's double slit experiment monochromatic light of wavelength Lambda the intensity of light at a point of path difference is Lambda by 3​

Answer 1

lambda is your answer

Answer 2

Answer:

So if monochromatic light in Young's double-slit experiment is replaced by white light, then the waves of every wavelength form their separate interference patterns. ... Hence the waves of all colors reach a middle point R in the same phase. So the central fringe is white.