Question

A beam of light of $\lambda =600$ nm from a distant source falls on a single slit $1$ mm wide and the resulting diffraction pattern is observed on a screen $2$m away. The distance between first dark fringes on either side of the central bright fringe is:

• A. $2.4$ cm
• B. $2.5$ cm
• C. $1.2$ cm
• D. $1.4$ mm

Answer 1

The correct option is A $2.4$ cm

Single slit experiment

Formula for fringewidth$=\lambda D/d$

slit width $d=0.001m=1mm,$

$\lambda =600nm$, $D=$screend istance$=2m$

So fringe width$=600nm\times \frac{2m}{0.001m}=1.2mm$

DIstance between two dark fringes which are on either side of the central bright fringe $=2\times 1.2mm=2.4mm$