(a) The interference pattern is not observed in Young's double slit experiment when the two sources S_1 and S_2 are far apart. Explain. (b) Mention…

a) Explanation $\displaystyle 1$

b) Condition for coherent source $\displaystyle 1$

c) Explanation $\displaystyle 1$

a) $\displaystyle \beta=\frac{\lambda D}{d}$, When space between point source increases, fringe width decrease. Interference pattern gets less and less sharp/ Interference pattern will not be observable. Alternatively On increasing separation between the slits the condition $\displaystyle \frac{s}{s}<\frac{\lambda}{d}$, will not be satisfied and interference pattern disappears.

b) Two sources must have same frequency and constant or zero phase difference / constant or zero path difference.

c) $\displaystyle \beta \propto \lambda$ fringe width will increase & intensity ( Brightness) of fringe will decrease.