Ncert Exercises & Solutions

10.21 In deriving the single slit diffraction pattern, it was stated that the intensity is zero at angles of nλ/a. Justify this by suitably dividing the slit to bring out the cancellation.

Hint: Use the concept of angle of diffraction.

Step 1: Find the width of each slit.

Consider that a single slit of width d is divided into n smaller slits.

∴ Width of each slit, $d^{'} = \frac{d}{n}$

Step 2: Find the angle of diffraction.
The angle of diffraction is given by the relation,

$θ = \frac{\frac{d}{d} λ}{d} = \frac{λ}{d}$

Each of these infinitesimally small slit sends zero intensity in direction 𝜃. Hence, the combination of these slits will give zero intensity.

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