Fringe width

 Fringe width

The distance between the center of two adjacent bright or dark bands is called as fringe width.

Fringe width of bright Bands: Let us consider two adjacent bright frindge at a distance xn  and  xn+1 from Central Bright.  Then according to Youngs experiment,

xn = (nλD)/d----------(1)

xn+1 =((n+1)λD)/d) ---------------(2)

xn+1 - xn   =((n+1) λD)/d) – (nλD)/d)

xn+1 - xn   =(n+1-n)  λD)/d

xn+1 - xn = (λD)/d

Fringe width of Dark Bands: Let us consider two adjacent Dark frindge at a distance xm  and  xm+1 from Central Bright.  Then according to Youngs experiment,

xm = ((2m-1) λD)/2d----------(1)

xm+1 =(2(m+1-1) λD)/2d)-----------(2)

xm+1 -  xm = (2(m+1)-1-2m+1) λD/2d)

xm+1 - xm = (λD)/d

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