Instruments to manipulate waves and reflection

When we talk about manipulating waves, we mean changing the direction, shape, focus, or behaviour of a wave using tools and instruments. Think about it: every time you look in a mirror, use a satellite dish, or speak into a megaphone, you are using an instrument that manipulates waves.

Waves — whether they are light waves, sound waves, or water waves — follow predictable rules. By understanding these rules, scientists and engineers have designed instruments that bend, bounce, focus, and redirect waves to do incredibly useful things.

In these notes, we will focus mainly on reflection — the bouncing of waves off surfaces — and the instruments built around it. We will also introduce lenses, which manipulate waves through a different behaviour called refraction.

Before diving into reflection, let's quickly recap some key wave properties you should already know — these will help you make sense of everything that follows.

• Wavelength ($\lambda$): The distance between two successive crests (or troughs) of a wave, measured in metres.
• Frequency ($f$): The number of complete waves passing a point per second, measured in hertz (Hz).
• Wave speed ($v$): How fast the wave travels through a medium, measured in m/s.

These three quantities are linked by the wave equation:

$v=f\times \lambda$

All types of waves — light, sound, water — can be reflected, refracted, and diffracted. In this unit, we are exploring how we can take advantage of these behaviours to build useful instruments.