Question
A screen is placed $50\,cm$ from a single slit which is illuminated with $6000\,\mathop A\limits^o $. If distance between first and third minima in the diffraction pattern is $3\,mm.$ What is the width of the slit ?
✓
Answer
$\mathrm{D}=50 \mathrm{\,cm}\, \lambda=600 \mathrm{\,nm}$
$y_{3}-y_{1}=\frac{3 D \lambda}{a}-\frac{D \lambda}{a}=\frac{2 D \lambda}{a}$
$3 \times 10^{-3}=\frac{2 \times 0.5 \times 600 \times 10^{-9}}{a}$
$a=0.2 \mathrm{\,mm}$
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