Question:
In a Young's double slit experiment 15 fringes are observed on a small portion of the screen when light of wavelength 500 nm is used. Ten fringes are observed on the same section of the screen when another light source of wavelength \(\lambda\) is used. Then the value of \(\lambda\) is (in nm) __________.
In a Young's double slit experiment 15 fringes are observed on a small portion of the screen when light of wavelength 500 nm is used. Ten fringes are observed on the same section of the screen when another light source of wavelength \(\lambda\) is used. Then the value of \(\lambda\) is (in nm) __________.
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Fringe width is proportional to wavelength, so the number of fringes in a fixed length is inversely proportional to wavelength.
Updated On: Nov 5, 2026
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Correct Answer: 750
Solution and Explanation
Fringe width \(\beta = \frac{\lambda D}{d}\). If the same length \(L\) of screen holds \(N\) fringes, \(L = N\beta = N\frac{\lambda D}{d}\), so \(N\lambda\) is constant.
\(15\times 500 = 10\times\lambda\), giving \(\lambda = 750\) nm.
Answer: 750
\(15\times 500 = 10\times\lambda\), giving \(\lambda = 750\) nm.
Answer: 750
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