1.11 - Reflection

Waves at a boundary - Absorbed, transmitted or reflected

When a wave reaches a boundary between two different materials, one of three things can happen:

1. Absorption - The wave's energy is transferred to the second material (for example, microwaves heating food).
2. Transmission - The wave carries on travelling through the new material, which often leads to refraction (a change in direction).
3. Reflection - The wave bounces back off the boundary instead of passing through or being absorbed.

Factors affecting the outcome:

• Which of these happens depends on the wavelength of the wave and the properties of the two materials.
• This applies to all types of wave, including electromagnetic waves, sound waves and water waves.

What reflection is

Reflection happens when a wave hits a boundary between two materials and bounces back, instead of being absorbed or passing into the new material.

Reflection happens with every kind of wave

• Light reflects off surfaces - it's how we see objects and how mirrors form images.
• Sound reflects off hard surfaces such as walls and cliffs, producing echoes.
• Water waves bounce back off a harbour wall or the side of a tank.

Hard surfaces reflect sound strongly, while softer surfaces absorb more of it and reflect less.