Wave pulse
Also called Pulse
A wave pulse is a single disturbance that transfers energy without transferring matter between two locations. Because it does not repeat, it has no wavelength and no frequency, only a shape, a speed and an amplitude.
Essential knowledge 14.1.A.1.i defines it in one line, and EK 14.1.A.1.ii supplies the contrast: a wave is modelled as a continuous, periodic disturbance with well defined wavelength and frequency. Flick a rope once and you send a pulse. Shake it steadily and you send a wave.
Why the CED bothers with the single case. A pulse makes boundary behaviour visible. With a continuous train, the incoming and reflected waves overlap everywhere and you see interference instead of the reflection itself. One pulse arrives, splits, and you can watch each part separately.
EK 14.3.A.1 says a wave crossing from one medium to another can be transmitted or reflected, depending on the properties of the boundary, and EK 14.3.A.1.i says both happen at once, using low mass and high mass strings as the example. Then the rule worth memorising:
- Reflected pulse inverted if the transmitted pulse travels into a medium in which the wave speed decreases (14.3.A.1.ii). Think light string into heavy string.
- Reflected pulse upright if the transmitted pulse travels into a medium in which the wave speed increases (14.3.A.1.iii).
Pulses pass through each other. EK 14.6.A.2: when two or more pulses interact they travel through each other and overlap rather than bouncing off each other, and EK 14.6.A.3 adds the displacements. That is superposition, and a pair of pulses is the cleanest place to see it, because before and after the overlap each pulse is unchanged.