Short Answer
L = nλ/2 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.
For fixed-fixed string: L = nλ/2, so only half-wavelengths fit. Fundamental mode (n=1): L = λ/2.
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. L = nλ
- B. L = nλ/2
- C. L = λ/n
- D. L = 2nλ
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.