Wave phase difference

We can describe the position of a wave using an angle: that’s called the phase of the wave.

The start of the wave is at 0 radians.

The next full cycle of the wave happens at 2\pi radians (360\degree).

This means that the phase difference between two peaks, troughs or wave cycles is 2\pi radians (360\degree).

Phase and antiphase

• If the phase difference between two points on a wave is 2\pi radians:

  • the points are in phase
  • the points are doing exactly the same thing

• If the phase difference between two points on a wave is \pi radians:

  • the points are in antiphase
  • the points are doing opposite things

Moving one wave by half a wavelength

If we move along a wave by half a wavelength, we move by a phase difference of \pi radians.

This means that if we start at a peak, and move half a wavelength along the wave, we’ll end up at a trough, for example.

• If the waves were previously in phase, they will now be in antiphase.
• If the waves were previously in antiphase, they will now be in phase.