Wave properties & types
Describe waves in terms of amplitude, wavelength, frequency, and wave speed; distinguish transverse waves (oscillation perpendicular to direction of travel) from longitudinal waves (oscillation parallel); and use the wave equation v = fλ
What a learner can do afterwards
- Identifies crest, trough, amplitude and wavelength from explicit descriptions and stated wave measurements
- Distinguishes transverse and longitudinal waves and gives an example of each
- Uses v = fλ to calculate wave speed, frequency, or wavelength given the other two
- Explains what happens to wavelength if frequency increases while wave speed stays constant
1 · Read
A crest is a wave's highest point, the peak you met before. A trough is its lowest point. Amplitude is the greatest displacement from rest. For a symmetric wave, peak-to-trough height is twice the amplitude. Wavelength, λ, is the distance along travel between neighbouring crests or troughs. Frequency counts cycles per second, not height. Stated crest positions let you find wavelength by subtraction.
In a transverse mechanical wave, material vibrates perpendicular to the wave's travel. For a horizontal rope shaken vertically, the rope moves up and down while the pattern travels along it. The rope is its medium; transverse does not mean that no medium is needed.
In a longitudinal mechanical wave, material vibrates parallel to the wave's travel. Sound in air is longitudinal: particles move back and forth as compressions and expansions travel. A spring pushed and pulled along its length also models longitudinal motion.
Use v = fλ: speed v (m/s) = frequency f (Hz) × wavelength λ (m). Hertz means cycles per second. Division undoes multiplication: f = v ÷ λ; λ = v ÷ f. At 28 m/s, wavelength 7 m gives 4 Hz, and 4 Hz gives 7 m. Divide centimetres by 100: 60 cm = 0.6 m. 0.7 is seven tenths: 5 × 0.7 = 35 ÷ 10 = 3.5. Subtract neighbouring crest positions to find λ.
At fixed speed, fλ stays constant. Doubling frequency halves wavelength; tripling frequency divides wavelength by three. At fixed frequency, doubling speed doubles wavelength.
Amplitude and wavelength can change independently. In light and radio waves, electric and magnetic fields oscillate perpendicular to travel without a material medium. Radio waves share light's vacuum speed. Real surface water waves can combine material motion parallel and perpendicular to travel, including horizontal and vertical motion.
Amplitude is the greatest displacement from rest. Wavelength is spacing between neighbouring matching points. The equation v = fλ links speed, frequency and wavelength.
Original extra questions and reading passages written for this learning dataset.
2 · Watch
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Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
20 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.