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

Explanation

Let `I_(1)=I_(2)=I`. If `phi` is phase difference between the two light waves, then resultant intensity.,
`I_(R)=I_(1)+I_(2)+2sqrt(I_(1)I_(2)). cos phi`
When path difference `=lambda,"Phase difference" phi=0^(@), therefore I_(R)=I+I+2sqrt(II), cos 0^(@)=4I=k`
When path difference `=lambda/3,"Phase difference" phi=(2pi)/(3) rad`,
`therefore I_(R)=I+I+2sqrt(II), cos ""(2pi)/(3) Rightarrow I_(R)=2I+2I((-1)/(2))=I=(K)/(4)`