In Young's double slit experiment using monochromatic light of wavelength `lamda`, the intensity of light at a point on the screen where path difference is `lamda` is K units. What is the intensity of light at a point where path difference is`(lamda)/3`?

Explanation

Inteference of waves from the two slits gives,
Intensity`I=I_(1)+I_(2)+2sqrt(I_(1)I_(2)). cos phi`
Phase difference `phi=(2pi)/(lamda)xx` path difference `=(2pi)/(lamda)xx lamda =2pi =0^(@)`
`:.` Intensity `I=I+I+2sqrt(I.I) . cos 0^(@)=I+I+3I=4I=K` units (given)
For path difference `(lamda)/3, phi=(2pi)/(lamda)xx(lamda)/3=(2pi)/3=120^(@)`
`:.` Intensity`I.=I+I+2sqrt(I.I). cos 120=I+I+2I(1/(-2))=I=I/4` (Unit)