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(a) The refractive index of glass is $1.5$. What is the speed of light in glass? (Speed of light in vacuum is $3.0 \times 10^8 \mathrm{~ms}^{-1}$ )
(b) Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?
(b) Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?
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Verified Answer
(a) Here, $\mathrm{n}=1.5, \mathrm{c}=3 \times 10^8 \mathrm{~ms}^{-1}$.
$$
\mathrm{v}=\frac{\mathrm{c}}{\mathrm{n}}=\frac{3 \times 10^8}{1.5}=2 \times 10^8 \mathrm{~ms}^{-1}
$$
(b) Speed of light in glass is not independent of the colour of light, because each colour of light has a chacteristic wavelength and speed of light as well as refractive index depends on wavelength.
The refractive index of violet colour is greater than the red colour hence the violet colour travels slower in a glass prism.
$$
\mathrm{v}=\frac{\mathrm{c}}{\mathrm{n}}=\frac{3 \times 10^8}{1.5}=2 \times 10^8 \mathrm{~ms}^{-1}
$$
(b) Speed of light in glass is not independent of the colour of light, because each colour of light has a chacteristic wavelength and speed of light as well as refractive index depends on wavelength.
The refractive index of violet colour is greater than the red colour hence the violet colour travels slower in a glass prism.
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