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Physics · 2025 · 2 marks
CBSE 2025 · Region 1 · Set 1 · Q18
(a) In a diffraction experiment, the slit is illuminated by light of wavelength 600 nm. The first minimum of the pattern falls at θ=30^°. Calculate…
(a)
In a diffraction experiment, the slit is illuminated by light of wavelength $\displaystyle 600$ nm. The first minimum of the pattern falls at $\displaystyle \theta=30^{\circ}$. Calculate the width of the slit.
OR
(b)
In a Young's double-slit experiment, two light waves, each of intensity $\displaystyle \mathrm{I}_{\mathrm{o}}$, interfere at a point, having a path difference $\displaystyle \frac{\lambda}{8}$ on the screen. Find the intensity at this point.
Marking-scheme solution
Condition for Minima
\[\mathrm{a} \sin \theta=\mathrm{n} \lambda
\]
For First Minima \(\displaystyle \mathrm{n}=1\)
\[\begin{gathered}
\mathrm{a} \sin 30^{\circ}=600 \times 10^{-9} \mathrm{~m} \\
\mathrm{a} \times \frac{1}{2}=600 \times 10^{-9} \mathrm{~m} \\
\mathrm{a}=1200 \times 10^{-9} \mathrm{~m} \\
=1.2 \times 10^{-6} \mathrm{~m}
\end{gathered}
\]
OR
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