Waves

Wave is a form of disturbance that travels through a material medium due to the repeated \(f\) periodic motion of the particles of the medium about their mean positions without any actual transportation of matter.

Waves transport energy and the pattern of disturbance has information that propagates from one point to another. All our communications essentially depend on the transmission of signals through waves. Speech means the production of sound waves in air and hearing amounts to their detection. Often, communication involves different kinds of waves. For example, sound waves may be first converted into an electric current signal which in turn may generate an electromagnetic wave that may be transmitted by an optical cable or via a satellite. Detection of the original signal will usually involve these steps in reverse order.

Not all waves require a medium for their propagation. We know that light waves can travel through vacuum. The light emitted by stars, which are hundreds of light years away, reaches us through interstellar space, which is practically a vacuum.

Characteristics of waves

The characteristics of waves are as follows:

1. The particles of the medium traversed by a wave execute relatively small vibrations about their mean positions but the particles are not permanently displaced in the direction of propagation of the wave.
2. Each successive particle of the medium executes a motion quite similar to its predecessors along/perpendicular to the line of travel of the wave.
3. During wave motion only the transfer of energy takes place but not that of a portion of the medium.

Waves are mainly of three types:

• Mechanical or elastic waves
• Electromagnetic waves and
• Matter waves.

Mechanical Waves

Mechanical waves can be produced or propagated only in a material medium. These waves are governed by Newton’s laws of motion. For example, the most familiar type of waves such as waves on a string, water waves, sound waves, seismic waves, etc. is the so-called mechanical waves. These waves require a medium for propagation, they cannot propagate through vacuum. They involve oscillations of constituent particles and depend on the elastic properties of the medium. Mechanical waves are of two types:

• Transverse wave motion.
• Longitudinal wave motion.

Electromagnetic Waves

These are the waves that require no material medium for their production and propagation, i.e., they can pass through vacuum and any other material medium. Electromagnetic waves do not necessarily require a medium, they can travel through vacuum. Light, radio waves, and X-rays, are all electromagnetic waves.

In vacuum, all electromagnetic waves have the same speed c, whose value is :
\(
c=299,792,458 \mathrm{~ms}^{-1} \dots(15.1)
\)

Matter waves

These waves are associated with moving particles of matter, like electrons, protons, neutrons, etc. Matter waves associated with electrons are employed in electron microscopes.