Q1. What is the minimum thickness of a soap bubble for which the first order of bright fringe is observed in reflected light? (2020)
Solution:
For the first order of bright fringe in reflected light, the minimum thickness of the soap bubble is λ/4 due to the phase change upon reflection.
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Q2. In a Newton's ring experiment, if the radius of the first dark ring is found to be r, what is the radius of the second dark ring? (2020)
Solution:
The radius of the dark rings in Newton's rings is proportional to the square root of the ring number. Thus, the second dark ring will have a radius of 2r.
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Q3. If the distance from the slits to the screen in a double-slit experiment is increased, what happens to the fringe pattern? (2023)
Solution:
Increasing the distance from the slits to the screen increases the fringe width, as fringe width β is proportional to the distance.
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Q4. In a diffraction pattern produced by a single slit, what happens to the central maximum when the slit width is decreased? (2022)
Solution:
Decreasing the slit width increases the diffraction angle, causing the central maximum to become wider.
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Q5. If the distance between the slits in a double-slit experiment is halved, what happens to the angular position of the first-order maximum? (2023)
Solution:
If the slit separation d is halved, the angle θ for the first-order maximum (d sin θ = λ) will increase, effectively doubling the angle.
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Q6. In a Newton's rings experiment, if the radius of the nth dark ring is r_n, what is the relationship between r_n and the wavelength λ? (2021)
Solution:
The radius of the dark rings in Newton's rings is given by r_n² = nλR, where R is the radius of curvature of the lens. Thus, r_n ∝ nλ.
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Q7. In a thin film of air between two glass plates, which of the following colors will be least affected by interference? (2022)
Solution:
Red light has the longest wavelength and is least affected by interference effects in thin films compared to shorter wavelengths.
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Q8. In a Michelson interferometer, what happens to the fringe pattern if one of the mirrors is moved away from the beam splitter? (2020)
Solution:
Moving one mirror changes the path length, causing the fringe pattern to shift to the right.
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Q9. In a thin film of oil on water, which color will appear at the center of the pattern if the film thickness is such that it causes destructive interference for red light? (2022)
Solution:
Destructive interference for red light means red light is canceled out, leaving the shorter wavelengths (blue) visible.
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Q10. In a thin film of soap, which color appears at the center of the pattern due to destructive interference? (2023)
Solution:
At the center, destructive interference occurs for red light due to its longer wavelength.
