CBSE 2023 · Region 5 · Set 2 · Q26 · 3 marks
A plane wave-front propagating in a medium of refractive index ' $\displaystyle \mu_{1}$ ' is incident on a plane surface making an angle of incidence (i). It enters into a medium of refractive index $\displaystyle \mu_{2}\left(\mu_{2}>\mu_{1}\right)$. Use Huygen's construction of secondary wavelets to trace the retracted wave-front. Hence verify Snell's law of refraction.Using Huygen's construction, show how a plane wave is reflected from a surface. Hence verify the law of reflection.
A plane wave-front propagating in a medium of refractive index ' $\displaystyle \mu_{1}$ ' is incident on a plane surface making an angle of incidence (i). It enters into a medium of refractive index $\displaystyle \mu_{2}\left(\mu_{2}>\mu_{1}\right)$. Use Huygen's construction of secondary wavelets to trace the retracted wave-front. Hence verify Snell's law of refraction.
Using Huygen's construction, show how a plane wave is reflected from a surface. Hence verify the law of reflection.
Marking-scheme solution
(a)
Tracing the refractive wavefront Verification of Snell's Law of refraction
AB is incident wavefront, incident at an angle i . let \(\displaystyle \tau\) be the time taken by wavefront to travel distance BC.
\(\displaystyle B C=\mathrm{v}_{1} \tau\) where \(\displaystyle \mathrm{v}_{1}\) is speed of wave in medium $\displaystyle 1$
To determine shape of refracted wavefront, we draw a sphere of radius \(\displaystyle \mathrm{v}_{2} \tau\),
Wave OpticsRefraction and Reflection of Plane Waves using Huygens PrincipleApplyshort_answerhard
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CBSE Class 12 Physics past-paper question from the 2023board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.