Calculate frequency, wave number, and period from a given wavelength.
Wi-Fi uses 12.5 cm (2.4 GHz) or 6 cm (5 GHz). Microwave ovens use 12.2 cm (2.45 GHz). Cell phones use 15-70 cm (430 MHz - 2 GHz). Visible light is 380-700 nm.
Wave number (k = 1/λ) counts how many complete waves fit in one meter. It's widely used in spectroscopy and optics. Higher wave number means shorter wavelength and higher energy.