CBSE 2025 · Region 4 · Set 3 · Q18 · 2 marks
In Young's double slit experiment, the screen is moved $\displaystyle 30$ cm towards the slits. As a consequence, the fringe width of the pattern changes by $\displaystyle 0.09$ mm . If the slits separation used is $\displaystyle 2$ mm , calculate the wavelength of light used in the experiment.
Marking-scheme solution
$\displaystyle \beta_{1}=\frac{D \lambda}{d}$
$\displaystyle \beta_{2}=\frac{D_{2} \lambda}{d}$
$\displaystyle \beta_{1}-\beta_{2}=\frac{\lambda}{d}\left(D_{1}-D_{2}\right)$
$\displaystyle =\frac{\lambda}{d}\left[D-\left(D-30 \times 10^{-2}\right)\right]$
$\displaystyle \lambda=\frac{\left(\beta_{1}-\beta_{2}\right) d}{30 \times 10^{-2}}=\frac{9 \times 10^{-5} \times 2 \times 10^{-3}}{30 \times 10^{-2}}$
$\displaystyle \lambda=6 \times 10^{-7} \mathrm{~m}$
Wave OpticsInterference of Light Waves and Young’s ExperimentApplyvery_short_answermedium
More from Wave Optics
- Assertion: In interference and diffraction of light, light energy reduces in one region producing a dark…2024 · asked 3×
- Assertion: In a Young's double-slit experiment, interference pattern is not observed when two coherent…2024 · asked 3×
- What are coherent sources? Why they are necessary for observing stable interference pattern? Draw a graph…2026 · asked 3×
- In a Young's double-slit experiment, the fringe width is found to be β. If the entire apparatus is immersed…2023 · asked 3×
- Assertion: In Young's double slit experiment all fringes are of equal width. Reason (R): The fringe width…2023 · asked 3×
- (i) A plane light wave propagating from a rarer into a denser medium, is incident at an angle i on the…2024 · asked 3×
- Assertion: Light added to light can produce darkness. Reason (R): When two coherent light waves interfere,…2026 · asked 3×
- In a Young's double-slit experiment, the screen is moved away from the plane of the slits. What will be its…2023 · asked 3×
CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.