Question

In Young's experiment two coherent sources are placed $0.90mm$ apart and fringe are observed one metre away. If it produces second dark fringes at a distance of $1mm$ from central fringe., the wavelength of monochromatic light is used would be

• A. $60\times {10}^{-4}cm$
• B. $10\times {10}^{-4}cm$
• C. $10\times {10}^{-5}cm$
• D. $6\times {10}^{-5}cm$

Answer 1

The correct option is D $6\times {10}^{-5}cm$

Formula,

$x=(2n-1)\frac{\lambda D}{2d}$

$\Rightarrow \lambda =\frac{2xd}{(2n-1)D}$

$=\frac{2\times {10}^{-3}\times 0.9\times {10}^{-3}}{(2\times 2-1)\times 1}$

$=6\times {10}^{-5}cm$