Question

Calculate the wave number of a photon whose wavelength is $400nm$.

• A. $0.001n{m}^{-1}$
• B. $0.002n{m}^{-1}$
• C. $0.0025n{m}^{-1}$
• D. $0.0045n{m}^{-1}$

Answer 1

The correct option is C $0.0025n{m}^{-1}$

Wavenumber of a wave is defined as $\tilde{\nu }=\frac{1}{\lambda }$, where $\lambda$ is the wavelength.

Given that wavelength of the photon is $\lambda =400\text{nm}=400\times {10}^{-9}\text{m}$

Thus, wave number is $\tilde{\nu }=(400{)}^{-1}{\text{nm}}^{-1}=0.0025{\text{nm}}^{-1}$