Question

Assuming expressions for path difference between two light waves for bright bands and dark bands, obtain an expression for the band width.

Answer 1

The path difference between two light waves interfering at a point is given by

`"Path difference" = (xd)/D`

The distance of n^th bright band from central bright band is given by

`x_n=D/dnlamda`

Distance of first bright band (n = 1),

`x_1=D/dlambda`

Similarly, distance of second bright band (n = 2),

`x_2=D/d2lambda`

`"Band width" = B = x_2-x_1=D/d2lambda-D/dlambda`

`= D/dlambda(2-1)=D/dlambda`

Similarly, we can find distance between two consecutive dark band and it is called Band width and is given by

`"Band width"=(Dlambda)/d`