Question
What are coherent sources? How does the width of interference fringes in Young’s double-slit experiment change when
(a) the distance between the slits and screen is decreased?
(b) frequency of the source is increased?
Justify your answer in each case.
Solution
Two sources which produce waves of same frequency and the phase difference of produced waves does not change with time i.e., they have zero or constant phase difference. These sources are said to be coherent sources.
Fringe width in young's double slit experiment is given by,
where,
D is the distance between the screen and the slit and,
d is the distance between the slits.
(a) Since, fringe width () has a direct dependence on D, fringe width decreases if the distance between the slits and screen is decreased.
(b) The fringe width decreases if, the frequency () of the source is increased because, fringe width and frequency have inversely dependent on each other.
Fringe width in young's double slit experiment is given by,
where,
D is the distance between the screen and the slit and,
d is the distance between the slits.
(a) Since, fringe width () has a direct dependence on D, fringe width decreases if the distance between the slits and screen is decreased.
(b) The fringe width decreases if, the frequency () of the source is increased because, fringe width and frequency have inversely dependent on each other.
