Question

In biprism experiment, the slit is illuminated by
a light of wavelength 4800 A. The distance
between the slit and biprism is 20 cm and the
distance between the biprism and eyepiece is
80 cm. If the distance between two virtual
sources is 0.30 cm. Determine the distance
between 56 bright band on one side of the
central band and 5 dark band on the other side.​

Answer 1

The distance  between 56 bright band on one side of the  central band and 5 dark band on the other side is 1.52 mM

Explanation:

x5 = nλD / d

x5 = 5Dλ / d (bright fringe)   ----(1)

x5' = (2n - 1) Dλ/ 2d (dark fringe)

x5' = 9Dλ / 2d    ----(2)

Now adding the both equations:

x5 + x5' = ( 5 + 9 / 2) Dλ / d

Now put the values:

x5 + x5' =  9 / 12 x 1 x 4800 x 10^-10 / 0.3 x 10^-3

x5 + x5' =  1.52 x 10^-3

x5 + x5' =  1.52 m M

Hence the distance  between 56 bright band on one side of the  central band and 5 dark band on the other side is 1.52 mM