What are coherent sources? Why are they necessary for observing stable interference pattern? Draw a graph showing the variation of intensity of light with the position on the screen in Young’s double-slit experiment.
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For sustained interference:
\[
\text{Coherent Sources}
\Longrightarrow
\text{Same Frequency + Constant Phase Difference}
\]
If the phase difference changes continuously, a stable interference pattern cannot be observed.