**Question 2.5: Yellow light emitted from a sodium lamp**

**Question 2.5: Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wave number (v¯****) of the yellow light.**

**Ans 2.5:** We know

λ = c/ ν

c = velocity of light (3 × 10^{8} m/s)

λ = Wavelength = 580 nm = 580 × 10^{-9} m

ν = c/ λ

ν = 3 × 10^{8} / 580 × 10^{-9}

ν = 5.17 × 10^{14} s^{-1}

Thus, the frequency of yellow light emitted from the sodium lamp = 5.17 × 10^{14} s^{–1}

The wave number (v¯) of yellow light is given by expression = 1/λ

= 1/580 × 10^{-9} m = 1.72 × 10^{6} m^{-1}

88

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