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The study of waves is a very important branch of physics because a great deal of our physical experience is due to this phenomenon. Your very reading of these lines is due to the light waves reflected from this page. When you are in the class room, the teacher’s voice reaches you in the form of sound waves. While watching the television or listening to the radio, have you ever thought that everything you see and hear is transmitted to you from the television station or the radio station in the form of waves.

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Figure 7.2 Ripple

Wave and Wave Motion

You would have observed disturbances produced on the surface of a pool of water when a stone is dropped (Figure 7.2). Also, plucking of the strings of certain musical instruments produces some sound. In these examples, disturbance produced at a point in space by a particle of the medium is handed to its neighbouring particle which in turn hands over its disturbance to its neighbouring particle and so on in succession. Each particle begins to vibrate a little later than the preceding particle. Thus, a propagating disturbance is set up in the medium.

The propagating disturbance set up in a medium is called a wave. The propagation of disturbance in the medium is called wave motion.

The study of waves is important since they can propagate energy and information through matter from one place to another without actual transportation of any matter.

Classification of Waves

Waves can be classified into several types based on the following two main criteria:
  1. whether or not they (waves) require a material medium for their propagation and
  2. the direction of vibration of the particles involved in the wave propagation.
  1. Based on requirement of material medium for propagation:

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  1. Based on the direction of vibration of the particles in the wave (Figures 7.3 and 7.4).

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Figure 7.3 An Example for Longitudinal Wave

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Figure 7.4 Transverse Wave

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  • Wavelength is also the distance travelled by a wave in unit time.
  • f represents the number of waves produced in one second, Description: 70071.png represents the time taken to produce one wave.
  • But time taken to produce one wave is also the period (T). Thus, Description: 70062.png.
  • Wavelength (m) is the distance travelled by a wave in a time equal to the period. Hence, wave velocity
    Description: 70055.png
    Since Description: 70047.png we have v = f m.

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