The figure shows a double slit experiment P and Q are the slits. The path lengths PX and QX are nλ and (n + 2) λ respectively, where n is a whole number and λ is the wavelength. Taking the central fringe as zero, what is formed at X

(1) First bright

(2) First dark

(3) Second bright

(4) Second dark

(3) For brightness, path difference =nλ=2λ

So second is bright.

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