Question

In a Young's double-slit experiment, a set of parallel slits with a separation of 0.134 mm is illuminated by light having a wavelength of 600 nm and the interference pattern observed on a screen 3.50 m from the slits.

(a) What is the difference in path lengths from the two slits to the location of a second order bright fringe on the screen?
μm

(b) What is the difference in path lengths from the two slits to the location of the second dark fringe on the screen, away from the center of the pattern?
μm

Answer 1

For part a) you need to use m = 3

δ=dsinθ=mλ = 1x 600 nm = 600 nm

. For part b) you need to use m = 2 because the first dark fringe is when the difference is one half a wavelength, ie m = 0. The second dark fringe will be when m = 1 and the third dark fringe will be when m = 2.

δ=dsinθ=(m+1/2)λ

= (1+0.5) x 600 = 900 nm

m 2 double slit m 0 source Each slit acts as a source of waves, the waves from the two slits interfere constructively or destructively at the screen screen m 2 pattern of lightand dark fringes observed on the screen