Question

A beam of light of wavelength 600 nm from distant source for a single slit 1 mm wide and resulting diffraction pattern is observed on a screen 2cm away. The distance between the First dark fringe on either side of the central Maximum is

Answer 1

For a dark fringe to be formed, $\frac {dy}{D}=\lambda$

$\lambda=600nm= 600\times 10^{-9}$

$d= 1mm= 10^{-3}$

$D=2m$ D=2m

$y=\frac {Dy}{d}= \frac {2\times 600\times10^{-9})}{10^{-3}}= 1.2mm$

The distance between the first dark fringe on either side of the central beam is

$2\times y= 2\times1.2= 2.4mm.$

Thus Answer is $2.4mm$