Question

A beam of light consisting of two wavelength $6300A^{\circ }$ and $\lambda A^{\circ }$ is used to obtain interference fringes in a Young’s double slit experiment. If $4^{th}$ bright fringe of $6300A^{\circ }$ coincides with $5^{th}$ dark fringe of $\lambda A^{\circ }$, the value of $\lambda$ (in $A^{\circ })$ is

• A. $5200$
• B. $4800$
• C. $6200$
• D. $5600$

Answer 1

The correct option is D $5600$

Given that $4^{th}$ bright fringe of $6300A^{\circ }$ coincides with $5^{th}$ dark fringe of $\lambda A^{\circ }$,
$n_1\times 6300=(2n_2-1)\lambda /2$
Here $n_1=4,n_2=5$
$4\times 6300=\left(4.5\right)\lambda$
$\lambda =\frac{4\times 6300}{9}\times 2=5600A^{\circ }$