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interference of monochromatic light


The first approximation for d<<x:

( x ± d/2 )2 ≅ x2 ± xd

The second approximation for d<<x<<L:

√ ( L2 + x2 ± xd ) ≅ L + ( x2 ± xd )/2L

Using those two approximations, we arrive at

1-2 ≅ xd/L

Using furthermore the relations of pages 15 and 18, we obtain for the positions of maxima on the screen

x = 0 , ± (λ/d) L , ±2 (λ/d) L , ...

The minima are in between.



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