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Edexcel GCSE Physics · 1PH0
Edexcel 1PH0 · 4.9P Check the specification (PDF) (opens in a new tab)
A wave carries energy towards a material interface: the boundary where two materials meet, such as air and glass or air and a wall. At that boundary, the wave need not have just one outcome. Some of its energy may return, some may pass into the second material, and some may be taken up by the material. These effects are called , and . A wave that passes into the second material may also be refracted.
At a boundary, portions of an incoming wave may be reflected, transmitted or absorbed. The transmitted portion may also refract.
In reflection, a wave travels back into the material it came from. You see light reflected by a mirror and hear an echo when sound reflects from a distant surface. The reflected wave still carries energy, but now travels away from the boundary. A boundary can reflect only part of an incoming wave while allowing another part through: a window, for example, can both reflect and transmit light.
Transmission means that a wave passes through a material or crosses into another one. Light transmitted through a clear window emerges on the other side. Sound transmitted through a wall can be heard beyond it, although it may be much quieter because not all the incoming sound energy gets through.
Refraction concerns the direction of a wave that crosses a boundary. If its speed changes on entering the second material, a wave arriving at an angle can change direction. Light entering glass from air is a familiar example. It is still transmitted into the glass: transmission describes its passage across the boundary, while refraction describes its change of direction. A wave meeting the boundary head-on can change speed without changing direction.
In absorption, energy carried by the wave is transferred to the material. For example, a dark curtain can absorb some incident light, warming slightly, rather than letting all the light through or reflecting it. A soft furnishing can absorb some sound energy, so less sound is reflected back into the room.
The material and the type of wave affect the balance between these outcomes. At one interface, a wave may be partly reflected, partly transmitted and partly absorbed; the transmitted part may also refract. Describing an interface therefore means identifying what happens to each part of the incoming wave, rather than assuming that every wave either bounces back or passes straight through.
Several effects can occur at the same boundary: an incoming wave can be partly reflected, transmitted and absorbed. Transmission and refraction can happen to the same part of the wave.
Describe what happens to the wave at the boundary: reflected waves return, transmitted waves pass through, and absorbed waves transfer energy to the material.
Do not treat transmission and refraction as alternatives: a wave can pass into a material and change direction.
A wave entering a new material does not always bend; if it meets the boundary head-on, it continues in the same direction.
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Last updated
Material interface
A boundary where one material meets another.
Reflection
The return of a wave from a boundary into the material it came from.
Refraction
A change in a wave’s direction as it passes from one material into another, caused by a change in speed.
Transmission
The passage of a wave through a material or across a boundary into another material.
Absorption
The transfer of energy from a wave to a material rather than that energy continuing in the wave.
Put your knowledge into practice — try past paper questions for Physics
Material interface
A boundary where one material meets another.
Reflection
The return of a wave from a boundary into the material it came from.
Refraction
A change in a wave’s direction as it passes from one material into another, caused by a change in speed.
Transmission
The passage of a wave through a material or across a boundary into another material.
Absorption
The transfer of energy from a wave to a material rather than that energy continuing in the wave.