Question

In Youngs double-slit experiment, distance between slits is $0.28\, mm$, distance between slits and screen is $1.4 \,m$ and distance between central bright fringe and third bright fringe is $0.9 \,cm$. 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=1.4\, m , n=3 $
$d=0.28 \,mm =0.28 \times 10^{-3} m $
$x_{3}=0.9\, cm =0.9 \times 10^{-2} m$
From the relation
$x_{3} =\frac{n D \lambda}{d} $
$\therefore \lambda =\frac{x_{3} \times d}{n D}=\frac{0.9 \times 10^{-2} \times 0.28 \times 10^{-3}}{3 \times 1.4}$
$=6 \times 10^{-7} m $
$=6000 \times 10^{-10} m$
$=6000\,\mathring{A}$