Calculate the wavelength, frequency and wave number of a light wave whose period is 2.0 × 10⁻¹² s.

(i) The frequency of the light wave is 1/period = 1/(2.0 × 10⁻¹² s) = 5 × 10⁹/s
(ii) The wavelength of light wave is c/ν = (3 × 10⁸ m/s)/(5 × 10⁹/s) = 6.0 × 10⁻² m
(iii) The wave number of light wave is 1/λ = 1/(6.0 × 10⁻²) = 16.66/m.