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Physics · 2026 · 4 marks
CBSE 2026 · Region 5 · Set 1 · Q30
In a Young's double-slit experiment, the two slits behave as coherent sources. When coherent light waves superpose over each other they create an…
In a Young's double-slit experiment, the two slits behave as coherent sources. When coherent light waves superpose over each other they create an interference pattern of successive bright and dark regions due to constructive and destructive interference. Two slits $\displaystyle 2$ mm apart are illuminated by a source of monochromatic light and the interference pattern is observed on a screen $\displaystyle 5 \cdot 0 \mathrm{~m}$ away from the slits as shown in the figure.
(i)
What property of light does this interference experiment demonstrate?
(A)
Wave nature of light
(B)
Particle nature of light
(C)
Transverse nature of light
(D)
Both wave nature and transverse nature of light
(ii)
(a)
The wavelength of light used in this experiment is :
(A)
$\displaystyle 720$ nm
(B)
$\displaystyle 590$ nm
(C)
$\displaystyle 480$ nm
(D)
$\displaystyle 364$ nm
OR
(b)
The fringe width in the interference pattern formed on the screen is :
(A)
1.$\displaystyle 2$ mm
(B)
0.$\displaystyle 2$ mm
(C)
4.$\displaystyle 2$ mm
(D)
6.$\displaystyle 8$ mm
(iii)
The path difference between the two waves meeting at point P, where there is a minimum in the interference pattern is:
(A)
$\displaystyle 8.1 \times 10^{-7} \mathrm{~m}$
(B)
$\displaystyle 7.2 \times 10^{-7} \mathrm{~m}$
(C)
$\displaystyle 6.5 \times 10^{-7} \mathrm{~m}$
(D)
$\displaystyle 6.0 \times 10^{-7} \mathrm{~m}$
(iv)
When the experiment is performed in a liquid of refractive index greater than $\displaystyle 1$ , then fringe pattern will :
(A)
disappear
(B)
become blurred
(C)
be widened
(D)
be compressed
Marking-scheme solution
(i)(A)
wave nature of light.
(ii)(a)
(C) $\displaystyle 480$ nm OR (b) (A) $\displaystyle 1.2$ mm
(iii)(B)
$\displaystyle 7.2 \times 10^{-7} \mathrm{~m}$
(iv)(D)
be compressed
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CBSE Class 12 Physics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.