S4.10.2 For the adult
Measuring waves
Kofi sends a wave along a rope. Ana asks how big the wave is. Where does Kofi put his ruler?
What this chapter teaches
Amplitude is measured from the rest line to a crest. Wavelength is crest to crest. Period is the time for one wave and frequency is waves each second, with f = 1 ÷ T. The speed of a wave is v = fλ, and the medium sets the speed.
Three questions to ask
There is no one right wording. Listen for the idea.
- Where do you measure the amplitude of a wave on a graph, and why is crest to trough not the amplitude?
- A wave has a frequency of 5 Hz and a wavelength of 2 m. How would you find its speed?
- If the frequency of a wave in a rope goes up, what happens to the wavelength, and why?
After the chapter, the learner can
- Label amplitude, wavelength and period on a wave diagram
- Calculate wave speed from frequency and wavelength
What they copy into their notebook
Amplitude: rest line to crest. Wavelength λ: crest to crest. Period T and frequency f = 1 ÷ T. Wave equation v = fλ. The medium sets v.