https://www.walter-fendt.de/html5/phen/standingwavereflection_en.htm
If the end is a fixed end, a 180° phase change occurs at the reflection. The incident and reflected wave superpose to form a standing wave that has a node at the fixed end.
–
If the end is a loose end, no phase change occurs at the reflection. The incident and reflected wave superpose to form a standing wave that has an antinode at the loose end.
