Question

Interference fringes are observed on a screen by illuminating two thin slits $1 mm$ apart with a light source $(\lambda=632.8 nm ) .$ The distance between the screen and the slits is $100 cm .$ If a bright fringe is observed on a screen at a distance of $1.27 mm$ from the central bright fringe, then the path difference between the waves, which are reaching this point from the slits is close to :

• A. $1.27 \mu m$
• B. $2 nm$
• C. $2.87 nm$
• D. $2.05 \mu m$

Answer 1

Answer: (A)

$y=\frac{n D \lambda}{d}$
$n=\frac{y d}{D \lambda}=\frac{1.27 \times 10^{-3} \times 10^{-3}}{1 \times 632.8 \times 10^{-9}}=2$
Path difference $\Delta x=n \lambda$
$=2 \times 632.8 nm$
$=1265.6 nm$
$=1.27 \mu m$