4.2 Wave motion(basics)

"Wave motion refers to the propagation of disturbances."

The easiest way to visualize is a water wave. When a water droplet is dropped in a still water, ripples travel out from the point where the droplets enters the water. The disturbance travels out from the center of the pattern, but the water does not travel with the wave. Here's an image of transverse wave motion produced by a water droplet on still water.

In physics wave motion can be classified into two types  
  • Mechanical waves and  
  • Electromagnetic waves.
Mechanical waves are waves in which physical disturbances require a physical medium for propagation. In case if above water wave, there can be no water wave if there is no water acting as a medium for disturbance. It can be further be classified into two types: Transverse waves and Longitudinal waves. More on these in other notes. Some examples of mechanical waves are sound waves(longitudinal type), waves on ropes(transverse type).

Electromagnetic waves are waves in which propagation of disturbances in electromagnetic fields, do not require a physical medium. Some example of electromagnetic waves are radio waves, microwaves, x-rays, visible lights and so on.

We now discuss a waveforms and wavefronts. All the medium's particles participating in the wave motion behave in the same manner, except that there is a progressive change in the phase of oscillation. The combined motions result in the advance of a pattern, called waveforms, in the direction of propagation. Whereas a wavefront is a surface over which a wave is at the same phase of oscillation at all points.

Here's what I meant. The wavefronts of a plane wave are planes as shown in the figure below. Waveform is a sinusoidal waveform.


In the two dimensional plane waves, the wavefronts are lines and the one-dimensional waves the wavefronts is a point (just take a single waveform).
We can also have a spherical wavefront as well,

Here's a basics on waves video,

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