Reflection, Refraction and Total Internal ReflectionAQA GCSE Physics: Revision notes

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

• Reflection — the wave bounces back off the surface.
• Absorption — the wave's energy is taken in by the material.
• Transmission — the wave passes through into the new material (often changing direction, i.e. refracting).

Ray diagrams can be used to represent reflection of a wave at a surface, showing the wave arriving at and leaving the boundary.

Different substances can absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength.

Refraction is the change in direction of a wave as it crosses a boundary between two different materials, caused by a change in the wave's speed in the new material. This can be shown using ray diagrams that illustrate the bending of a ray at the boundary between two media.

Differences in the velocity, absorption and reflection of waves as they pass through different solids and liquids can be used to detect and explore what lies beneath a surface. Examples include:

• Ultrasound — high-frequency sound waves reflected from boundaries inside the body to build up an image.
• Echo sounding — sound waves reflected off the sea floor or underwater objects, used to measure depth.
• Seismic waves — used to explore the structure of the Earth (see below).

Earthquakes produce two types of seismic wave that travel through the Earth and are reflected and refracted at boundaries between different layers:

• P-waves — longitudinal waves that can travel through both solids and liquids.
• S-waves — transverse waves that can travel through solids but cannot travel through liquids.

By studying how these waves are reflected, refracted, and where they stop being detected around the globe, scientists have found evidence for the size and structure of the Earth's core — including the discovery that part of the core must be liquid, since S-waves do not pass through it.