Question

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

• A. First bright
• B. First dark
• C. Second bright
• D. Second dark

Answer 1

Answer: (C)

Second bright

Answer 2

For brightness, path difference $= n\lambda = 2\lambda$

So second is bright.