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noppawit

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**Two isotropic (radiating the same intensity of EM wave in all directions) point sources S**

At what value of x

_{1}and S_{2}emit light in phase at wavelength λ and at the same amplitude. The sources are separated by distance 2d=6.00λ. They lie on the axis that parallel to the x-axis, which runs along a viewing screen at distance D=2.00λ. The origin lies on the perpendicular bisector between the sources. The figure below shows two rays reaching point P on the screen, at position x_{p}At what value of x

_{p}do the rays have the minimum possible phase difference?http://www.wisheyebio.com/images/screen.png

From question, the minimum possible phase difference, does it mean that the first dark point, or not?

I tried like this...

[tex]\Delta L=d\sin \theta) = (m+0.5)\lambda[/tex]

[tex]\frac{2dx_{p}}{D} = 0.5\lambda[/tex]

[tex]\frac{6 \lambda x_{p}}{20\lambda}[/tex]

[tex]x_{p} = 1.66\lambda[/tex]

Am I correct or not?

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