## Comprehensive Question 4: What is wave motion? How waves can be categorized?

### Waves

A progressive wave is a disturbance of some kind which moves from the source point to the surrounding places, and as a result, energy is transferred from one place to another. So, we can define a wave as, “a mechanism of disturbance, moving outward from its origin, and transferring energy by means of vibration of the medium and no transport of the medium particles.

Thus for a wave, we have;

• A disturbance in the form of vibrating particles of the medium.
• Energy is transferred from one place to another in the medium, but the medium particles just vibrate about their mean positions.

Wave motion and oscillations are related. When the wave moves through a medium, the particles of the medium perform simple harmonic motion. As an example, drop a stone in a water pond. A pattern of waves starts from the point of impact and spreads out to farther points. Drop a piece of paper in the area. You will see the paper does not go along the wave. It just oscillates back and forth about the mean position and the waves pass on.

### Categorization of waves

There are two types of waves as far as their origination is concerned.

• Mechanical Waves: “Waves produced by the oscillation of some material body and creating disturbance in the surrounding elastic medium”.

Examples of such waves are water waves. Water waves are produced when some material body is continuously oscillating in water and produce waves.

• Electromagnetic Waves: “Electromagnetic waves are produced by the oscillation of alternating electric and magnetic fields”.

This type of waves is a combination of traveling electric and magnetic fields. Both electric and magnetic fields are perpendicular on each other and the wave travels in a direction perpendicular to both the fields. For example, if electric field is along x-direction of a coordinate system, magnetic field is along the y-direction, then the wave travels in the z-direction of the coordinate axes.

Similarly, waves can also be categorized on the basis of the oscillation of the medium particles.

• Transverse Waves: “Waves in which the particles of medium oscillate perpendicular to the motion of the wave are called transverse waves.”

Water waves is a good example of transverse waves. Water particles (or molecules) oscillate perpendicular to the direction of motion of the wave. Waves in a rope are also transverse waves.

• Longitudinal Waves: “Waves in which the particles of the medium oscillate parallel to the direction of motion of the wave are called longitudinal waves.”

Sound waves is a good example of longitudinal waves. The air particle (or any other medium particles) oscillate along the direction of motion of the wave.