What a wave moves and what it leaves behind, the two kinds of wave, and reading amplitude, wavelength, frequency and period.
What you will learn
- Tell a transverse wave from a longitudinal one
- Read amplitude and wavelength from a wave diagram
- Use T = 1/f to link period and frequency
Waves move energy, not stuff
Drop a stone in a pond and a leaf floating nearby bobs up and down as the ripples pass, then settles where it started.
The ripples carried energy across the pond; the water itself did not travel with them.
That is true of every wave: it transfers energy (and often information) from one place to another without carrying the medium along.
There are two kinds, told apart by the way the vibrations (oscillations) go:
- Transverse: the vibrations are at right angles to the direction the energy travels. Ripples on water, waves on a string, and every electromagnetic wave (light, radio, X-rays) are transverse.
- Longitudinal: the vibrations are along the same direction the energy travels. Sound is longitudinal, and so is ultrasound, sound too high for us to hear. The medium bunches up into compressions and spreads out into rarefactions.
C marks a compression and R a rarefaction. One wavelength is the distance from one compression to the next.
A slinky spring shows both. Move one end from side to side and the coils vibrate at right angles to the wave: transverse. Push and pull the end along the slinky and the coils bunch and spread along it: longitudinal. Earthquakes make both kinds too: P-waves are longitudinal and S-waves are transverse.
Electromagnetic waves can travel through a vacuum (empty space). Sound needs a medium (a solid, liquid or gas) to pass through.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Waves move energy, not stuff
- Reading a wave diagram
- Frequency and period
- Try it: Read a wave graph
7 practice questions, marked as you go; about 20 minutes in all.
Key terms
Energy, Compressions, Rarefactions, P-waves, S-waves, Time, Period
In this unit: Waves and the electromagnetic spectrum
Transverse and longitudinal waves, v = fλ and the wave practicals, reflection and refraction, and the electromagnetic spectrum with its uses, dangers and the infrared practical.
- Transverse and longitudinal waves
- Wave speed and measuring waves
- Reflection and refraction
- The electromagnetic spectrum
- Uses and dangers of electromagnetic waves