Reflection is the change in direction of a wave at a point between two different mediums so that the wave returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves.
Fixed-end reflection is when the wave is inverted from a rigid obstacle. In this reflection, a pulse with a crest will reflect off the end and return with a trough of the same amplitude. This inversion behaviour will always be observed when the end of the medium is fixed. This inversion behaviour is also observed when the medium is connected to another more heavy or more dense medium. In the latter case, when the pulse reaches the end of the medium, a portion of the pulse will reflect off the end and return with an inverted displacement. The heavier medium acts like a fixed end to cause the pulse to be inverted. The amplitude, wavelength and frequency do not change in this reflection, the only effect is that a trough turns into a crest and a crest turns into a trough.
Free end reflection is when the new medium is free to move and there is no inversion. That is, a pulse with a trough will reflect off the end and return with the same upward displacement as a trough. Sometimes it is said that the pulse is not inverted. This behaviour of non-inversion will always be observed when the end of the medium is free to move. This behaviour of non-inversion is also seen when the medium is connected to another less heavy or less dense medium. In the this case, when the pulse reaches the end of the medium, a portion of the pulse will reflect off the end and return with the same direction of displacement; it is not inverted. When the wave reflects in the other direction, the wavelength, amplitude and frequency do not change; instead they stay the same. The second wave will be reflected and then continue on to the other medium. Since the medium beyond the end is less dense and less heavy, it fails to fix the medium's end and thus allows it to move; in this sense, the end of the medium behaves as a free end.
Fixed-end reflection is when the wave is inverted from a rigid obstacle. In this reflection, a pulse with a crest will reflect off the end and return with a trough of the same amplitude. This inversion behaviour will always be observed when the end of the medium is fixed. This inversion behaviour is also observed when the medium is connected to another more heavy or more dense medium. In the latter case, when the pulse reaches the end of the medium, a portion of the pulse will reflect off the end and return with an inverted displacement. The heavier medium acts like a fixed end to cause the pulse to be inverted. The amplitude, wavelength and frequency do not change in this reflection, the only effect is that a trough turns into a crest and a crest turns into a trough.
Free end reflection is when the new medium is free to move and there is no inversion. That is, a pulse with a trough will reflect off the end and return with the same upward displacement as a trough. Sometimes it is said that the pulse is not inverted. This behaviour of non-inversion will always be observed when the end of the medium is free to move. This behaviour of non-inversion is also seen when the medium is connected to another less heavy or less dense medium. In the this case, when the pulse reaches the end of the medium, a portion of the pulse will reflect off the end and return with the same direction of displacement; it is not inverted. When the wave reflects in the other direction, the wavelength, amplitude and frequency do not change; instead they stay the same. The second wave will be reflected and then continue on to the other medium. Since the medium beyond the end is less dense and less heavy, it fails to fix the medium's end and thus allows it to move; in this sense, the end of the medium behaves as a free end.