Chemistry / Unit 5 Chem 0769 worked example, 60 to 90 seconds
Solving c = λν for Frequency
The idea
Solving the relation c = λν for frequency means dividing the fixed speed of light by a wave's known wavelength, after converting that wavelength to meters.
In practice
A sodium streetlight emits light at a wavelength λ of 589 nm, and the goal is its frequency ν in hertz. First convert: λ = 589 nm = 5.89 × 10⁻⁷ m. Substituting into ν = c / λ gives ν = (2.998 × 10⁸ m/s) / (5.89 × 10⁻⁷ m). The meters cancel, leaving units of 1/s, or hertz. Carrying out the division gives ν ≈ 5.09 × 10¹⁴ Hz. Checking the result: visible light frequencies fall near 10¹⁴–10¹⁵ Hz, so this value sits in the right range for light a person can see.
Where people slip
Leaving the wavelength in nanometers instead of converting to meters before dividing produces a frequency wrong by nine orders of magnitude.
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