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Science · 2024 · 2 marks
CBSE 2024 · Region 2 · Set 1 · Q24
State two laws of refraction of light.Define the term absolute refractive index of a medium. A ray of light enters from vacuum to glass of absolute refractive index 1.5. Find the speed of light in glass. The speed of light in vacuum is $\displaystyle 3 \times 10^{8} \mathrm{~m} / \mathrm{s}$.
State two laws of refraction of light.
Define the term absolute refractive index of a medium. A ray of light enters from vacuum to glass of absolute refractive index 1.5. Find the speed of light in glass. The speed of light in vacuum is $\displaystyle 3 \times 10^{8} \mathrm{~m} / \mathrm{s}$.
Marking-scheme solution
Laws of Refraction of light :
(i)
The incident ray, the refracted ray and the normal to the interface of
two transparent media at the point of incidence, all lie in the same plane.
(ii)
The ratio of the sine of angle of incidence to the sine of angle of
refraction is a constant, for the light of a given colour and for the given
pair of media.
Absolute refractive index of a medium is the ratio of speed of light in
air/vacuum to the speed of light in the given medium.
Given:
\[\mathrm{c}=3 \times 10^{8} \mathrm{~m} / \mathrm{s} ; \mathrm{n}_{\mathrm{m}}=1 \cdot 5 ; \mathrm{v}_{\mathrm{m}}=?
\]
Absolute refractive index of a medium $\displaystyle \left(\mathrm{n}_{\mathrm{m}}\right)$
\[\begin{aligned}
& =\frac{\text { speed of light in vacuum }}{\text { speed of light in medium }}=\frac{c}{v_{m}}
\mathrm{v}_{\mathrm{m}}=\frac{c}{n_{m}}=2 \times 10^{8} \mathrm{~m} / \mathrm{s} &
\end{aligned}
\]
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CBSE Class 10 Science past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.