Reflectie van golven

When a propagating wave encounters the boundary of any medium, it gets reflected. The wave from the source, propagating in air, that hits the boundary of the medium is called the incident wave. The outgoing wave is called the reflected wave.

Now, consider propagation of waves through a stretched string, tied at one end to a hook on the wall. The wave travels to the hook and gets reflected.

Since the boundary of the medium is not free to move with the oscillations of the wave, it is called a fixed boundary condition.

In such a case, the reflected wave is 180° out of phase with respect to the incident wave.

Assuming no losses have occurred, the amplitude of the reflected wave remains unchanged.

When the boundary of the medium is free to move with the wave's oscillations, it is called a free boundary condition.

In such a case, the reflected wave has the same amplitude and phase as the incident wave.