# (solved)Question 2.5 of NCERT Class XI Chemistry Chapter 2

Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wavenumber (ν) of the yellow light.
(Rev. 03-Aug-2022)

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### Question 2.5 NCERT Class XI Chemistry

Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wavenumber (ν) of the yellow light.

### Video Explanation(detailed solution given after this video)

Please watch this youtube video for a quick explanation of the solution:

### Solution in Detail

$\displaystyle \underline{\underline{\text{Part (i)}}}$

speed of light $\displaystyle c = 3 \times 10^8 \text{m/s}$

Given: wavelength $\displaystyle \lambda = 580 \times 10^{-9} m$

frequency $\displaystyle \nu = \frac{c}{\lambda}$

$\displaystyle = \frac{3 \times 10^8}{580 \times 10^{-9}}$

$\displaystyle = 5.17 \times 10^{14}\text{ Hz }\underline{Ans}$

$\displaystyle \underline{\underline{\text{Part (ii)}}}$

Wave number $\displaystyle \overline{\nu} = \frac{1}{\lambda} (\text{m}^{-1})$

$\displaystyle = \frac{1}{580 \times 10^{-9}} = 1.7 \times 10^6 \text{ m}^{-1}\:\underline{Ans}$