Light from a He-Ne laser ( = 632.8 nm ) strikes a pair of slits at normal incide

Question

Light from a He-Ne laser ( = 632.8 nm ) strikes a pair of slits at normal incidence, forming a double-slit interference pattern on a screen located 2.00m from the slits. The figure(Figure 1) shows the interference pattern observed on the screen. What is the slit separation? d=____um

Light from a He-Ne laser ( = 632.8 nm ) strikes a pair of slits at normal incidence, forming a double-slit interference pattern on a screen located 2.00m from the slits. The figure(Figure 1) shows the interference pattern observed on the screen. What is the slit separation? d=____um

Explanation / Answer

In interfreence or diffraction pattern

the needed equation is Y = mLR/d---------------1

and d sin theta = mL--------------------2

where L = wavelgnth

m = order = 1,2,3,4, ......... for brigth bands

m = 1.5, 2.5, 3.5, 4.5, ......for dark bands

R is the distance from slit to screen

Y = disatnce from central spot to nth order fringe or fringe width

so here we apply

apply Y = mLR/d

d = mLR/Y

d = 4 * 632.8 nm * 2/(23mm)

d = 220 um

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