In a biprism experiment,monochromatic light of wavelength $\lambda$ is used. The distance between the two coherent sources $d$ is kept constant. If the distance between the slit and the eyepiece $D$ is varied as $D_1, D_2, D_3, D_4$ and the corresponding measured fringe widths are $W_1, W_2, W_3, W_4$,then:

• A
  $W_1 D_1 = W_2 D_2 = W_3 D_3 = W_4 D_4$
• B
  $\frac{W_1}{D_1} = \frac{W_2}{D_2} = \frac{W_3}{D_3} = \frac{W_4}{D_4}$
• C
  $W_1 \sqrt{D_1} = W_2 \sqrt{D_2} = W_3 \sqrt{D_3} = W_4 \sqrt{D_4}$
• D
  $D_1 \sqrt{W_1} = D_2 \sqrt{W_2} = D_3 \sqrt{W_3} = D_4 \sqrt{W_4}$