Question

In Youngs double slit experiment, the slits are $2mm$ apart and are illuminated with a mixture of two wavelengths $\lambda =12000A^o$ and $\lambda =10000A^o$. At what minimum distance from the common central bright fringe on a screen $2m$ from the slits will a bright fringe from one interference coincide with a bright fringe from the other?

• A. $3.2mm$
• B. $6.0mm$
• C. $7.2mm$
• D. $9.2mm$

Answer 1

The correct option is B $6.0mm$

$n\lambda \frac{D}{d}=(x-1){\lambda }^{\prime }\frac{D}{d}$
$n=5$; $x=6.0mm$
Hence $\left(B\right)$ is correct.