Summary
A wave is a disturbance that spreads and carries energy, but not matter, from one place to another. Sound and light are waves. Waves have amplitude, related to intensity, and frequency, related to pitch in sound and to colour in light.
Sound is a mechanical wave: it needs a medium (air, water) to travel, which is why nothing is heard in a vacuum. Light is an electromagnetic wave and does travel through a vacuum, which is why the Sun's light reaches us. Light can be reflected, bouncing like in a mirror, or refracted, changing direction when passing from one medium to another, like the pencil that looks broken in water. White light is made of all the colours, as seen in the rainbow.
Key points
- A wave carries energy, not matter.
- Sound and light are waves.
- Amplitude (intensity) and frequency (pitch in sound, colour in light).
- Sound is a mechanical wave: it needs a medium (it does not travel in a vacuum).
- Light is an electromagnetic wave: it does travel in a vacuum.
- Light reflects (bounces) and refracts (bends when changing medium).
- White light contains all the colours (the rainbow).