. P OLARISATION Consider holding a long string that is held horizontally, the other end of which is assumed to be fixed. If we move the end of the string up and down in a periodic manner, we will generate a wave propagating in the + x direction (Fig. .
). Such a wave could be described by the following equation FIGURE . (a) The curves represent the displacement of a string at t = and at t = t , respectively when a sinusoidal wave is propagating in the + x -direction. (b) The curve represents the time variation of the displacement at x = when a sinusoidal wave is propagating in the + x -direction.
At x = x , the time variation of the displacement will be slightly displaced to the right.