Question

A light wave is incident normally over a slit of width $24\times {10}^{-5}cm$. The angular position of second dark fringe from the central maxima is ${30}^o$. What is wavelength of light?

• A. $6000\mathring{A}$
• B. $5000\mathring{A}$
• C. $3000\mathring{A}$
• D. $1500\mathring{A}$

Answer 1

The correct option is A $6000\mathring{A}$

For second dark fringe,

$d\sin \theta =2\lambda$

$\Rightarrow$ $24\times {10}^{-5}\times {10}^{-2}\times \sin {30}^o=2\lambda$

$\Rightarrow$ $\lambda =6\times {10}^{-7}m$ $=6000\mathring{A}$