Short Answer
2π/λ is the best answer.
Wave and optics questions test how frequency, wavelength, phase, interference, and geometry fit together. Start with the physical picture before choosing the equation.
Wavenumber k = 2π/λ; it represents the spatial frequency of the wave in rad/m.
Why This Answer Is Correct
This is a Medium-level question in Waves & Optics. The prompt is really testing whether you can connect the concept to its defining physical relationship instead of picking a nearby-but-wrong term.
If a waves question feels messy, sketch the geometry or phase relationship first, then return to the algebra.
Choices At A Glance
- A. λ/2π
- B. 2π/λ
- C. 1/λ
- D. πλ
When similar options appear on an exam, eliminate the ones that break the core law, use the wrong units, or confuse a definition with a consequence.
Topic Snapshot
Topic: Waves & Optics
Difficulty: Medium
Best next move: Re-state the governing law in your own words, then solve one more example from the same topic before moving on.