8.1.4—Wavelength may be determined from the positions of nodes or antinodes of a

In a stationary wave, adjacent nodes or adjacent antinodes are separated by λ/2; a node to the nearest antinode is λ/4.

Measure over several intervals when possible, divide by the number of half-wavelength gaps, then multiply by two.

Four adjacent node gaps spanning 12 cm give λ=2×(12/4)=6.0 cm.

Counting positions rather than gaps gives an off-by-one error; the end-to-end distance must be divided by the number of intervals.