SL and HL: When a wave reaches a boundary between two media, some energy may be reflected, while some may be transmitted into the second medium. If the transmitted wave changes speed and enters at an angle, it also undergoes refraction.
The Mechanism
The incident wave carries energy toward the boundary. The properties of the two media determine how this energy is divided between the reflected and transmitted waves; some energy may also be absorbed.
| Process | What happens |
|---|---|
| Reflection | The wave remains in the original medium and travels away from the boundary. The angle of reflection equals the angle of incidence, with both measured from the normal. |
| Transmission | The wave crosses the boundary and continues through the second medium, usually with reduced amplitude because only part of the incident energy is transmitted. |
| Refraction | The transmitted wave changes direction because its speed changes at the boundary. Refraction occurs only if the wave enters obliquely; at normal incidence, its speed changes without a change in direction. |
The frequency is fixed by the source, so it does not change at the boundary. From