Question:
In a double-slit experiment, green light (5303 Å) falls on a double slit having a separation of \(19.44\ \mu\mathrm{m}\) and a width of \(4.05\ \mu\mathrm{m}\). The number of bright fringes between the first and the second diffraction minima is :
In a double-slit experiment, green light (5303 Å) falls on a double slit having a separation of \(19.44\ \mu\mathrm{m}\) and a width of \(4.05\ \mu\mathrm{m}\). The number of bright fringes between the first and the second diffraction minima is :
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Diffraction minima occur at \(a\sin\theta = n\lambda\) and interference maxima at \(d\sin\theta = m\lambda\); count the integers \(m\) lying between \(d/a\) and \(2d/a\).
Updated On: Nov 5, 2026
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- 05
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- 09
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The Correct Option is B
Solution and Explanation
First diffraction minimum: \(a\sin\theta_1 = \lambda\); second: \(a\sin\theta_2 = 2\lambda\).
Interference maxima: \(d\sin\theta = m\lambda\), so at the minima \(m = \frac{d}{a}\) and \(m = \frac{2d}{a}\).
\(\frac{d}{a} = \frac{19.44}{4.05} = 4.8\), and \(\frac{2d}{a} = 9.6\).
Orders strictly between 4.8 and 9.6: \(m = 5, 6, 7, 8, 9\), i.e. 5 bright fringes.
Answer: (2) 05
Interference maxima: \(d\sin\theta = m\lambda\), so at the minima \(m = \frac{d}{a}\) and \(m = \frac{2d}{a}\).
\(\frac{d}{a} = \frac{19.44}{4.05} = 4.8\), and \(\frac{2d}{a} = 9.6\).
Orders strictly between 4.8 and 9.6: \(m = 5, 6, 7, 8, 9\), i.e. 5 bright fringes.
Answer: (2) 05
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