x = (1/6)l at the required point

Therefore Px = (2/l) sin2 (npx/l)

Px = (2/3X0.15) sin2 [2p(1/6)l/l]

= (2/0.45) sin2 (p/3) = 3.33 nm-1

P = Px dx = (3.33 nm-1)(0.0030 nm) = 0.010

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