Question

In certain Young’s double slit experiment, the slit separation is 0.05 cm. The slit to screen distance is 100 cm. When blue light is used, the distance from central fringe to the fourth order bright fringe is 0.36 cm. What is the wavelength of blue light ?

• A. $4000 \mathring{A}$
• B. $4300 \mathring{A}$
• C. $4400 \mathring{A}$
• D. $4500 \mathring{A}$

Answer 1

Answer: (D)

Here, $ d $ = 0.05 cm, $D$ = 100 cm
$x$ = 0.36 cm, $n$ = 4
For bright fringes, $x = \frac{n \lambda D}{d} $ or $\lambda = \frac{xd}{nD}$
Substituting the values, we get
$\lambda = \frac{\left(0.36 cm \right)\times \left(0.05 cm\right)}{4 \times\left(100 cm\right)}$
$ = 4.5 \times 10^{-5} \, cm = 4.5 \times 10^{-7} m = 4500 \mathring{A}$