Question

(i) What is the effect on the interference fringes to the Young’s double slit experiment when
(a) the separation between the two slits is decreased?
(b) the width of the source-slit is increased?
(ii) The intensity at the central maxima in Young’s double slit experimental setup is I₀. Show that the intensity at a point where the path difference is λ/3, is I₀/4.

Answer 1

➡Double slits produce two coherent sources of waves that interfere. (a) Light spreads out (diffracts) from each slit, because the slits are narrow. These waves overlap and interfere constructively (bright lines) and destructively (dark regions). We can only see this if the light falls onto a screen and is scattered into our eyes. (b) Double slit interference pattern for water waves are nearly identical to that for light. Wave action is greatest in regions of constructive interference and least in regions of destructive interference. (c) When light that has passed through double slits falls on a screen, we see a pattern such as this. (credit: PASCO)

Answer 2

Assertion: In Young's double slit experiment using white light, the central fringe is white, the violet coloured fringe will be seen nearest to the central fringe. Reason: Red coloured fringe will be seen near central fringe.