question_answer

A beam of light of wave length 6000 A 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 the first dark fringes on either side of the central bright fringe is

A)  2.4 cm           

B)  1.2 cm

C)  2.4 mm            

D)  1.2 mm

Correct Answer: C

Solution :

: For diffraction, when the pattern is obtained on a screen at distance\[(f)\], \[\frac{x}{f}=\frac{\lambda }{a}\] or\[x=\frac{f\lambda }{a}=\]Distance of first dark fringe from axis. \[\therefore \] = 0.12 cm = 1.2 mm \[\therefore \]\[2x=\]Distance between the first dark fringes on either side of the central bright fringe \[\therefore \]Distance\[=2.4\text{ }mm\]