Introduction

A wave is something you have already met in several everyday forms — water waves, sound waves, light waves — as well as under the broader headings mechanical waves and electromagnetic waves. A mechanical wave is a disturbance produced in an elastic medium by the periodic vibration of the medium's own particles about their respective mean (rest) positions. As this disturbance passes from one particle to the next, it carries energy and momentum along with it — a wave genuinely transfers energy from one point to another — but it does not transfer any matter: no particle of the medium is bodily carried along with the wave, each one only oscillates about the position it already occupied.

Electromagnetic (EM) waves are a distinct second category: unlike mechanical waves, they do not require a material medium to propagate through at all, which is why they are called non-mechanical waves — this is what lets them travel through empty space.

You have already studied sound waves — which are mechanical waves — along with their properties and phenomena such as echo, reverberation and the Doppler effect, in earlier classes. This chapter builds on that foundation and studies mechanical waves further: how a wave reflects when it meets a boundary between two media, the principle of superposition (the rule for combining two or more overlapping waves into one resultant disturbance), and the phenomena superposition produces — stationary (standing) waves and beats — together with their applications.