Properties of Wave Motion

Two types of graphs can be used to represent wave motion.  
  • Displacement-Distance Graph
  • Displacement-Time Graph
    •   

    Displacement-Distance Graph

    Crest: highest point of a wave.

    Trough: lowest point of a wave.

    Amplitude, A: maximum distance from the rest or central position, in either direction.
    • SI Unit: m
    • Scalar quantity

    Wavelength, λ: shortest distance between two consecutive crests or troughs of a wave or any two points that are in phase.
    • SI unit: m       
    • Scalar quantity

    Phase: any two points are in phase when they move in the same direction with same speed and have same displacement from the rest or central position. i.e D and B are in phase, but not with C.

    Displacement-Time Graph

    Period, T: time taken to form one complete wave. 
    • SI unit: s

    Frequency. f: number of complete waves produced per second.
    • SI unit: Hertz (Hz)
    • Scalar quantity
    • Frequency is source dependent. 

    Formula: f = 1 / T.

    Wave Speed

    Wave Speed, v: distance traveled by a wave per unit time.
    • SI Unit: m/s
    • Scalar quantity
    • Formula: v = f λ 

    Speed of wave affected by the depth.
    Depth Frequency Wavelength Speed
    Shallow Remains the same Short Slow
    Deep Remains the same Long Fast

    Wavefront

    Wavefront: an imaginary line joining all the crests or troughs in a wave.
    • Formula: number of complete wave = number of wavefront – 1 

    Prediction on particle movement

    • To determine the movement of a particle in transverse wave, we have to sketch another wave in the wave direction.
    • For longitudinal wave, it is much more complicated and will be discussed in Sound.

    Example:

    The diagram shows a traverse wave on a string with two points P and Q marked. The wave is moving in the direction shown. What will happen next to particle P and Q?
    Excel@Physics