Wave motion (A) What is a wave? Wave is a way of transferring energy by means of vibration. Waves transfer energy without a transfer of matter. (B) Transverse wave and longitudinal wave Waves can be classified into transverse waves and longitudinal waves according to the direction of vibration. A transverse wave is one in which the vibrations are at right angles to the direction of travel of the wave. Examples: water waves, light. A longitudinal wave is one in which the vibrations are along the direction of travel of the wave. Example: sound. (C) Terms for describing a wave The amplitude A of a wave is the size of maximum disturbance measured from the resting position. The wavelength λ of a wave is the minimum distance in which a wave repeats itself. The frequency f of a wave is the number of complete waves produced in one second. It is also the number of vibrations completed by a particle in the wave. It is measured in hertz (Hz). The frequency of a wave is determined by the vibrating source. Wave motion 1 The period T of a wave is the time taken for one wave to be produced. It is also the time taken for a particle on the wave to make one complete vibration. T = 1 . The T period of a wave is determined by the vibrating source. The wave speed v is the distance travelled by the wave in one second. It is determined by the medium of the wave, except in the case of electromagnetic waves in which the wave speed also depends slightly on frequency. (D) Relationship between wave speed, frequency and wavelength The relationship between wave speed v, frequency f and wavelengthλ is given by the equation v = f λ. (E)Vibrations in wave motion Particles which are one wavelength apart vibrate in phase; particles which are half a wavelength apart vibrate in antiphase. For example, in the following transverse wave, particles a, i and g are vibrating in phase and a and e are vibrating antiphase. When a particle on a wave makes one complete vibration, the wave moves forwards a distance equal to one wavelength. A displacement-time graph shows the displacements of a particle on a graph at different times. A displacement-distance graph shows the displacements of all the particles on a wave at a certain time. (It should be noted that these two types of graph are totally different.) Wave motion 2