MECHANICAL WAVES Mechanical waves are the vibration of particles.
This means that they need a medium to travel through. Examples: waves in water, waves on a rope, sound waves
Electromagnetic (EM) Waves ELECTROMAGNETIC WAVES
Electromagnetic (EM) waves are the disturbance/vibration of electric and magnetic (electromagnetic) fields.1
Light wave M E
= wavelength E = amplitude of electric field M = amplitude of magnetic field
Distance Fig 10.4: EM waves Travelling Waves
As a wave is observed travelling through a medium, a crest is seen moving along from left to right or vice versa.This crest is followed by a trough, which is in turn followed by the next crest. In fact, one would observe a distinct wave pattern (in the form of a sine wave) travelling through the medium.2 This sine wave pattern continues to move in uninterrupted fashion. Although the entire wave appears to be moving in one direction continuously, the particles that produce the wave are merely vibrating ‘up and down’ or ‘back and forth’; there is no net movement of the particles.The term ‘periodic’ is used because there is a regularly repeating pattern.
TERMS USED TO DESCRIBE PERIODIC TRAVELLING WAVES
Periodic travelling waves are a regularly repeating cycle that appears to move in the direction of propagation of the wave. A crest is the highest point of a transverse wave. A trough is the lowest point of a transverse wave. An oscillation (or cycle) is one complete vibration of the source.
1Electromagnetic waves will be dealt with in more detail in Chapter 14. 2As well as travelling waves, there are also stationary waves which will be dealt with in the next chapter. WAVES 157 Wavelength
Direction of propagation Fig 10.5: Transverse and longitudinal travelling waves
