The Supporting Physical Concepts to understand the above topics are given below;
1. The superposition principle
2. The Pythagoras Theorem
3. The condition for constructive and destructive interference in terms of path difference
These are the only 3 physical concept that support the main topic if clear to you no problem to understand it.
The fringe with is the distance between two consecutive bright or dark fringes, that denoted by beta. Here to derive it we use the path difference between two rays which reaches at the point P from the slit S1 and S2 .
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