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Physics · 2022 · 3 marks
CBSE 2022 · Region 2 · Set 2 · Q10
(a) Is the speed of light in glass independent of the colour of light? Give reason. (b) A small bulb is placed at the bottom of a tank containing…
(a)
Is the speed of light in glass independent of the colour of light ? Give reason.
(b)
A small bulb is placed at the bottom of a tank containing water to a depth of $\displaystyle 70$ cm. Find the area of the surface of water through which light from the bulb can emerge out. Given refractive index of water is $\displaystyle \frac{4}{3}$.
Marking-scheme solution
a) No $\displaystyle \mu \alpha \frac{1}{\mathrm{v}_{\mathrm{m}}} \alpha \frac{1}{\lambda}$ Where $\displaystyle \mathrm{v}_{\mathrm{m}}$ velocity of light in medium ∴ velocity depends on wavelength
b) 
$\displaystyle \mu \sin \theta_{C}=1 \Rightarrow \sin \theta_{C}=\frac{1}{\mu}=\frac{3}{4} \tan \theta_{C}=\frac{r}{h}=\frac{1}{\mu} \times \frac{1}{\sqrt{1-\dfrac{1}{\mu^{2}}}}=\frac{1}{\sqrt{\mu^{2}-1}}$
Area $\displaystyle A=\pi r^{2}=\pi\left(h \tan \theta_{c}\right)^{2} A=\frac{\pi h^{2}}{\mu^{2}-1}$
$\displaystyle A=\frac{\pi \times 70 \times 70}{\left(\dfrac{4}{3}\right)^{2}-1}=19800 \mathrm{~cm}^{2}$All Ray Optics and Optical Instruments questions2022 question paperNCERT solutions: Ray Optics and Optical InstrumentsPractice Ray Optics and Optical Instruments →
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CBSE Class 12 Physics past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.