A beam of light travels from air into a ...

CBSE Class 12 Physics 2023 Outside Delhi Set 1 Paper

Question : 9 of 35

Marks: +1, -0

A beam of light travels from air into a medium. Its speed and wavelength in the medium are

1.5 \times 10^{8}

\mathrm{ms}^{-1}

and

230\ \mathrm{nm}

respectively. The wavelength of light in air will be

Solution: 👈: Video Solution

In the medium

c = n \lambda

or,

1.5 \times 10^{8} = n \times 230 \times 10^{-9}

or,

n = \frac{1.5 \times 10^{8}}{230 \times 10^{-9}}

\therefore n = \frac{1.5}{230} \times 10^{17}\ \mathrm{Hz}

In air,

Frequency remains unchanged. So,

n = \frac{1.5}{230} \times 10^{17}\ \mathrm{Hz}

v' = n \lambda'

\text{ or, } 3 \times 10^{8} = \frac{1.5}{230} \times 10^{17} \times \lambda'

\therefore \lambda' = 3 \times \frac{230}{1.5} \times 10^{-9}

= 460\ \mathrm{nm}

\;

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