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Question
A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1 m away. It is observed that the first minimum is a distance of 2.5 mm away from the centre. Find the width of the slit.
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Solution
\[\text { Distance of first minimum y } = \frac{\lambda}{a}\]
\[ \Rightarrow\text { slit width a } = \frac{\lambda}{y}\]
\[ \therefore a = \frac{500 \times {10}^{- 9}}{2 . 5 \times {10}^{- 4}} = 0 . 002 m\]
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