Monochromatic light waves of wavelength $λ$ from two coherent sources fall on a large plane screen. One of the waves is emanated from a point source S located at distance L from the screen and other one is a broad plane wave as shown in the figure.
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Question

Monochromatic light waves of wavelength $λ$ from two coherent sources fall on a large plane screen. One of the waves is emanated from a point source S located at distance L from the screen and other one is a broad plane wave as shown in the figure.

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Infinity Learn · Accepted Answer

Let say nth bright fringe is forming at point P  Path difference, Δx $$=$$ $$SP-$$ RP $$=$$ nλ ⇒Δ$$x=L2+r2$$− $$L=n$$λ ⇒$$L2+r2=n$$λ$$+L$$ ⇒$$L2+r2=n2$$λ$$2+L2+2n$$λL ⇒$$r=2n$$λL        [∵$$n2$$λ$$2$$ may be neglected]  ∴rn $$=$$ $$2n$$λL      and   rn−$$1=2(n$$−$$1)$$λL  Spacing between them $$=$$ rn $$-$$  rn−$$1$$                                           $$=$$ $$2n$$λL $$-$$ $$2(n$$−$$1)$$λL                                           $$=2$$λ$$L(n$$−n−$$1)$$

Monochromatic light waves of wavelength $λ$ from two coherent sources fall on a large plane screen. One of the waves is emanated from a point source S located at distance L from the screen and other one is a broad plane wave as shown in the figure.
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Monochromatic light waves of wavelength λ from two coherent sources fall on a large plane screen. One of the waves is emanated from a point source S located at distance L from the screen and other one is a broad plane wave as shown in the figure. Mark the correct options

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Monochromatic light waves of wavelength $λ$ from two coherent sources fall on a large plane screen. One of the waves is emanated from a point source S located at distance L from the screen and other one is a broad plane wave as shown in the figure.
Mark the correct options