Definition
Transverse wave: particles vibrate perpendicular to the direction the wave travels (e.g. a wave on a rope, light).
Longitudinal wave: particles vibrate parallel to (along) the direction the wave travels, forming compressions and rarefactions (e.g. sound).
Mechanical waves (sound, water waves) need a medium to travel; electromagnetic waves (light) do not — this is exactly why sound can't cross empty space but light can.
Remember
A wave transfers energy from one place to another without transferring matter — the medium's particles oscillate about a fixed position rather than travelling with the wave.
Definition
Wavelength (): the distance between two consecutive identical points (e.g. crest to crest).
Frequency (): the number of complete waves passing a point per second.
Amplitude: the maximum displacement from the rest position — a larger amplitude means the wave carries more energy.
( = time period, the time for one complete wave)
Example 1 — wave speed
A wave has wavelength m and frequency Hz. Find its speed.
- .
Answer: m/s
Example 2 — frequency from time period
A wave's time period is s. Find its frequency.
- .
Answer: Hz
Definition
Refraction: a wave changes speed (and usually direction) when it enters a medium where it travels at a different speed — as a tsunami approaches shallow water, its speed decreases and its wavelength shortens (frequency stays the same).
Diffraction: a wave spreads out after passing through a gap or around an obstacle — most noticeable when the gap is close to the wave's own wavelength in size. This is why sound (long wavelength) diffracts around a corner or wall easily, letting you hear someone you can't see.
Quick Recap
- ●Transverse: perpendicular vibration. Longitudinal: parallel vibration (compressions/rarefactions)
- ●Mechanical waves need a medium; electromagnetic waves don't
- ●A wave transfers energy, not matter
- ●; ; larger amplitude more energy
- ●Refraction: speed/direction change entering a new medium. Diffraction: spreading through a gap, strongest when gap wavelength
