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JEE Mains · Physics · STD 12 - Wave optics
  • JEE Mains 2017
  • Medium
  • Numerical

A single slit of width \(0.1\, mm\) is illuminated by a parallel beam of light of wavelength \(6000\,\mathop A\limits^o \) and diffraction bands are observed on a screen \(0.5\, m\) from the slit. The distance of the third dark band from the central bright band is........\(mm\)

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Answer & Solution

Correct Answer

(B) \(9\)

Step-by-step Solution

Detailed explanation

\(\mathrm{a}=0.1\, \mathrm{mm}=10^{-4}\, \mathrm{cm}\)

\(\lambda=6000 \times 10^{-10}\, \mathrm{cm}=6 \times 10^{-7} \,\mathrm{cm}, \mathrm{D}=0.5\, \mathrm{m}\)

for \(3^{\text {rd }}\) dark band, \(a\,\sin \theta=3 \lambda\)

or \(\sin \theta=\frac{3 \lambda}{a}=\frac{x}{D}\)

The distance of the third dark band from the central bright band

\(x = \frac{{3\lambda D}}{a}\) \( = \frac{{3 \times 6 \times {{10}^{ - 7}} \times 0.5}}{{{{10}^{ - 4}}}}\) \(=\,9\,mm\)

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