Which formula expresses speed (m/s) in terms of frequency and wavelength?

Which formula expresses speed (m/s) in terms of frequency and wavelength?

• A. Speed (m/s) = wavelength (m) / frequency (Hz)
• B. Speed (m/s) = frequency (Hz) x wavelength (m)
• C. Speed (m/s) = frequency (Hz) + wavelength (m)
• D. Speed (m/s) = frequency (Hz) - wavelength (m)

Answer: (B)

The key idea is that the speed of a wave is how far it travels in one second. Frequency tells how many cycles occur each second, and wavelength tells how far the wave travels in one cycle. Put together, in one second the wave covers f cycles × λ meters per cycle, so the speed is v = f × λ. The units line up: Hz is 1/s and meters per cycle is meters, so Hz × meters gives meters per second. The other forms don’t match the distance-per-time relationship: dividing would mix the units to something like meters per second times seconds, and adding or subtracting doesn’t describe distance traveled per time. For a concrete check, if f = 500 Hz and λ = 0.6 m, v = 500 × 0.6 = 300 m/s.

The key idea is that the speed of a wave is how far it travels in one second. Frequency tells how many cycles occur each second, and wavelength tells how far the wave travels in one cycle. Put together, in one second the wave covers f cycles × λ meters per cycle, so the speed is v = f × λ. The units line up: Hz is 1/s and meters per cycle is meters, so Hz × meters gives meters per second. The other forms don’t match the distance-per-time relationship: dividing would mix the units to something like meters per second times seconds, and adding or subtracting doesn’t describe distance traveled per time. For a concrete check, if f = 500 Hz and λ = 0.6 m, v = 500 × 0.6 = 300 m/s.