A light of wavelength of \( 6 \times 10^{-7}\,\mathrm{m} \) illuminates a single slit of width 1.2 mm. The screen is at a distance of 2.4 m away from the slit. The width of central maximum is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 2.4 mm
In single-slit diffraction the first minima lie at angles \( \pm\lambda/a \) on either side of the centre, so the central maximum spans twice that angle.
\( \displaystyle w = \frac{2\lambda D}{a} \)
\( \lambda = 6\times10^{-7}\,\mathrm{m} \)
\( D = 2.4\,\mathrm{m} \)
\( a = 1.2\,\mathrm{mm} = 1.2\times10^{-3}\,\mathrm{m} \)
\( \displaystyle w = \frac{2 \times 6\times10^{-7} \times 2.4}{1.2\times10^{-3}}\,\mathrm{m} = 2.4\times10^{-3}\,\mathrm{m} = 2.4\,\mathrm{mm} \)