The wave number $\bar{\nu}$ of electromagnetic radiation is defined as
- $\bar{\nu} = c\lambda$
- $\bar{\nu} = \lambda/c$
- $\bar{\nu} = 1/\lambda$
- $\bar{\nu} = \lambda$
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Correct answer: C. $\bar{\nu} = 1/\lambda$
Wave number is the number of waves per unit length, i.e. the reciprocal of wavelength: $\bar{\nu} = 1/\lambda$ in $m^{-1}$ (or $cm^{-1}$ in spectroscopy).