Question

What is the effect on the interference fringes in a Young's double slit experiment when (i) the width of the two slits is increased (ii) the monochromatic source is replaced by a source of white light and (iii) the separation between the two slits is increased, keeping other variables constant in each case?

Answer 1

(i) : Intensity of light emitted by the slits increases as the width of the slit is increased. Thus, more brighter fringes are formed at the screen on increasing the width of the slits.

(ii) : Coloured fringes are formed at the screen if monochromatic light is replaced by the white light.

(iii) : Fringe width $\beta =\frac{\lambda D}{d}$

So, width of the fringes gets decreased if the distance between the slits $\left(d\right)$ is increased and thus we get narrower fringes.