A double-slit arrangement produces straight, equidistant fringes on a screen kept far away. Answer the following:
(i) State what is meant by fringe width in an interference pattern.
(ii) A student claims that the number of complete bright fringes contained between two points on the screen depends only on the distance between those points and not on where the segment lies with respect to the central maximum. Give reasons to accept or reject the claim.
(iii) Why is it necessary to speak of “complete” fringes while counting them over a chosen segment of the screen? Explain with the help of a labelled sketch showing an interval that starts and ends within two successive bright fringes.