Question

What will happen to
1- fringe separation
2- position of fringe pattern

if one of the two slits in Young's double slit experiment are covered with glass and why?

Answer 1

the glass slide will slow the passage of light, thus effectively increasing Δx between the two light paths, so the fringe separation increases and position of pattern changes

Answer 2

Umm... Increasing path difference causes fringe separation to inc? That's not right.
And, to which side the pattern shifts?
Would appreciate if somebody could elaborate.

Answer 3

first of all the position of pattern will change. Usually the highst Intensity is in the middlle between the slits, that is because in the middle both rays travel the same distance(more specifically optical path).
putting glass infront of one will change this. becasue one ray will travel through it slower, and the phase between the two will change.

Answer 4

about the seperation i think it will be smaller, since the smaller d is (between the two slits) the larger the seperation, right?
checked it now, will decrease. since the black spots are given by
\[\theta=\lambda /2d \]
and the glass chages in to something like
\[\theta=\lambda /(2d*n)\] \[n >1\]

Answer 5

walter lewin gives a very good simple and intersting lecture about this and how to derive it

Answer 6

since glass is a denser medium the ray of light wile coming out of glass bends away from the normal. so the fringe shifts in the direction of the slit before which the glass slab is placed. assuming the glass slab is placed before the upper slit, the fringe pattern shifts upward.\[s=(\mu-1)t D/d\]