A linear aperture whose width is 0.02 cm is placed immediately in front of a lens of focal length 60 cm. The aparture is illuminated normally by a parallel beam of wavelength 5 × 10 - 5 cm. The distance of the first dark band of the diffraction pattern from the centre of the screen is (a) 0.10 cm (b) 0.25 cm (c) 0.20 cm (d) 0.15 cm

Answer: (d). First dark band: y = (fλ)/(a). y = 60 × 5×10⁻⁵0.02 = 0.15 cm. So the answer is (d) 0.15 cm.

A linear aperture whose width is 0.02 cm is placed immediately in… | NEET 2016 (Phase 2)

Q76NEET 2016 · PHASE 2Easy

Diffraction at a Single Slit

A linear aperture whose width is 0.02 cm is placed immediately in front of a lens of focal length 60 cm. The aparture is illuminated normally by a parallel beam of wavelength 5 $\times$ 10 $-$ 5 cm. The distance of the first dark band of the diffraction pattern from the centre of the screen is

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Answer: (d)

First dark band: $y = \frac{f\lambda}{a}$ .
$y = \frac{60 \times 5\times10^{-5}}{0.02} = 0.15\ \text{cm}$ .
So the answer is (d) 0.15 cm.

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