CBSE Class 12 Physics 2023 Outside Delhi Set 1 Paper - Question ...

CBSE Class 12 Physics 2023 Outside Delhi Set 1 Paper

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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 × 10^8

{\ms}^{-1}

and

230 {\nm}

respectively. The wavelength of light in air will be

$230 {\nm}$
$345 {\nm}$
$460 {\nm}$
$690 {\nm}$

Solution:

In the medium

c\;=n λ

or,

1.5 × 10^8\;=n × 230 × 10^{-9}

or,

n\;=\;{1.5 × 10^8}/{230 × 10^{-9}}

∴ n\;=\;{1.5}/{230} × 10^{17} {\Hz}

In air,
Frequency remains unchanged. So,

n\;=\;{1.5}/{230} × 10^{17} {\Hz}

v^{'}\;=n λ^{'}

\;\;\text " or, "\; \;\; 3 × 10^8=\;{1.5}/{230} × 10^{17} × λ^{'}

\; ∴ \;\; λ^{'}=3 × \;{230}/{1.5} × 10^{-9}

\;=460 {\nm}

\;

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