12. In Young’s double slit experiment the distance between the slits and the screen is doubled. The separation between the slits is reduced to half. As a result the fringe width :

12. In Young’s double slit experiment the distance between the slits and the screen is doubled. The separation between the slits is reduced to half. As a result the  fringe width :

(a) is doubled

(b) is halved

(c) becomes four times

(d) remains unchanged

Answer :  (c) becomes four times

\( \beta = \frac{\lambda D}{d} \)

\( \beta_2 = \frac{\lambda \, 2D}{d/2} \)

\( = 4 \frac{\lambda D}{d} \)

\( = 4\beta \)