Question

In Youngs double-slit experiment, distance between slits is $0.28mm$, distance between slits and screen is $1.4m$ and distance between central bright fringe and third bright fringe is $0.9cm$. What is the wavelength of light used?

• A. $5000\mathring{A}$
• B. $6000\mathring{A}$
• C. $7000\mathring{A}$
• D. $9000\mathring{A}$

Answer 1

Answer: (B)

Given $:D=1.4m,n=3$
$d=0.28mm=0.28\times 10^{-3}m$
$x_3=0.9cm=0.9\times 10^{-2}m$
From the relation
$x_3=\frac{nD\lambda }{d}$
$\therefore \lambda =\frac{x_3\times d}{nD}=\frac{0.9\times 10^{-2}\times 0.28\times 10^{-3}}{3\times 1.4}$
$=6\times 10^{-7}m$
$=6000\times 10^{-10}m$
$=6000\mathring{A}$