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Physics · 2025 · 3 marks
CBSE 2025 · Region 4 · Set 2 · Q26
(a) Define 'wavefront' of a light wave. A plane wavefront is refracted from a convex lens. Draw the shape of the refracted wavefront. (b) A plane…
(a)
Define 'wavefront' of a light wave. A plane wavefront is refracted from a convex lens. Draw the shape of the refracted wavefront.
(b)
A plane wave travelling in a medium is incident on a plane surface separating this medium from a rarer medium. Draw a diagram to show refraction of the wave. Hence, verify Snell's law.
Marking-scheme solution
(a)
Wavefront – It is a continuous locus of points at which all the particles of the medium are vibrating in the same phase.
(b)
Considering triangles ABC and AEC:
$\displaystyle \sin i=\frac{B C}{A C}=\frac{v_{1} \tau}{A C}$ -----($\displaystyle 1$)
$\displaystyle \sin r=\frac{A E}{A C}=\frac{v_{2} \tau}{A C}$ -----($\displaystyle 2$)
$\displaystyle \frac{\sin i}{\sin r}=\frac{v_{1}}{v_{2}}=\frac{n_{2}}{n_{1}}$
$\displaystyle n_{1} \sin i=n_{2} \sin r$
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CBSE Class 12 Physics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.