# A beam of light $\lambda =600 nm$ 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: Option 1) 1.2 cm Option 2) 1.2 mm Option 3) 2.4 cm Option 4) 2.4 mm

Answers (1)
V Vakul

As we learnt in

Fraunhofer Diffraction -

$b\sin \theta = n\lambda$

- wherein

Condition of nth minima.

$b=$ slit width

$\theta =$ angle of deviation

distance between first daic fringe on both side means width of central maxima

$\therefore\Delta y = \frac{2\lambda D}{b}=\frac{2\times600\times10^{-9}\times2m}{10^{-3}m}$

$\Deltay=2.4mm$

Option 1)

1.2 cm

This is incorrect option

Option 2)

1.2 mm

This is incorrect option

Option 3)

2.4 cm

This is incorrect option

Option 4)

2.4 mm

This is correct option

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