Maths With Matt · Interactive Physics
Standing Waves & Reflection
Watch an incident wave reflect from a boundary and superpose with the reflected wave. Switch between fixed and free ends, change the wave, and identify the nodes and antinodes.
What is happening?
The wave travelling towards the boundary is the incident wave. At the boundary it is reflected. The incident and reflected waves occupy the same region of space, so their displacements add by the principle of superposition.
Fixed end
A reflection from a fixed end undergoes a phase change of 180°. The boundary must always have zero displacement, so there is a node at the fixed end.
Free end
A reflection from a free end does not undergo the 180° phase change. The displacement is maximum at the free boundary, so the boundary is an antinode.
A-Level Physics checkpoints
Node: a point that remains at zero displacement. Antinode: a point at which the oscillation amplitude is maximum. Adjacent nodes are separated by λ/2, while a node and its nearest antinode are separated by λ/4.
Try changing the wavelength while keeping the length of the displayed region fixed. Notice how the spacing of the nodes changes. Then switch the boundary from fixed to free and observe what happens at the reflecting end.