Two coherent sources ' $\mathrm{P}$ ' and ' $\mathrm{Q}$ ' produce interference at point ' $\mathrm{A}$ ' on…
Two coherent sources ' $\mathrm{P}$ ' and ' $\mathrm{Q}$ ' produce interference at point ' $\mathrm{A}$ ' on the screen, where there is a dark band which is formed between $4^{\text {th }}$ and $5^{\text {th }}$ bright band. Wavelength of light used is $6000 Å$. The path difference PA and QA is
$3.6 \times 10^{-4} \mathrm{~cm}$
$3.2 \times 10^{-4} \mathrm{~cm}$
$2.4 \times 10^{-4} \mathrm{~cm}$
$2.7 \times 10^{-4} \mathrm{~cm}$
Solution
The dark band between the $4^{\text {th }}$ and $5^{\text {th }}$ bright band in the $5^{\text {th }}$ dark band.
For $5^{\text {th }}$ dark band, the path difference is
$\left(5-\frac{1}{2}\right) \lambda=4.5 \lambda=4.5 \times 6000=2.7 \times 10^{-4} \mathrm{~cm}$