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Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wave number (`bar v`) of the yellow light.

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#### Solution

From the expression,

`lambda = "c"/"v"`

We get,

`"v" = "c"/lambda` ....(i)

Where,

ν = frequency of yellow light

c = velocity of light in vacuum = 3 × 10^{8} m/s

λ = wavelength of yellow light = 580 nm = 580 × 10^{–9} m

Substituting the values in expression (i):

`"v" =(3xx10^8)/(580xx10^(-9)) = 5.17 xx 10^14 "s"^(-1)`

Thus, frequency of yellow light emitted from the sodium lamp

= 5.17 × 10^{14} s^{–1}

Wave number of yellow light, `barv = 1/lambda`

`= 1/(580xx10^(-9)) = 1.72 xx 10^6 "m"^(-1)`

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