Question

Figure (17-E5) shows three equidistant slits being illuminated by a monochromatic parallel beam of light. Let BP₀ — AP₀,= λ/ 3 and D >> λ. (a) Show that in this case d=√(2Dλ/3). (b) Show that the intensity at P₀ is three times the intensity due to any of the three slits individually.

Answer 1

So, it can be said that light from B and C are in same phase as they have some phase difference with respect to A.

(using vector method)

As, the resulting amplitude is √3 times, the intensity will be three times the intensity due to individual slits.