General Properties Of Waves — study notes

Drop two pebbles into a still pond a second apart and watch the rings spread outward. Nothing about the water itself reaches the far bank — yet plainly something is getting there. That something is energy, and pinning down exactly what moves (and what doesn't) is the key to this whole O-Level Physics topic.

What A Wave Actually Carries

A wave is a mechanism for shifting energy from one spot to another without shifting the stuff it passes through. Picture a long line of dominoes toppling one after another: each domino barely strays from where it started, yet the collapse itself races along the entire row. A wave behaves the same way — every particle of the medium (that stuff the wave passes through) jiggles around a fixed resting spot while the disturbance marches onward past it.

That jiggle can point in one of two directions relative to where the wave is heading, and this split matters enormously for exams. When the wiggle runs side to side, at right angles to the wave's path, the wave is transverse — light and ripples on water behave this way. When the wiggle runs forward and back, along the very line the wave is travelling, the wave is longitudinal — sound moves this way, as a chain of squeezed and stretched regions pushing through the air.

Once you can picture the jiggle, three numbers pin down how a wave behaves: the furthest a particle strays from its resting spot (amplitude), how long one full repeat of the pattern stretches (wavelength), and how many repeats sweep past a fixed spot each second (frequency, counted in hertz — 6 Hz means six repeats per second). Multiply the last two together and you get how briskly the whole pattern advances — its speed.

Worked Example — Speed of a Ripple-Tank Wave

1. A vibrating bar dips into a ripple tank. Note the givens before anything else: f = 6 Hz, λ = 0.3 m.
2. Recall the rule linking the three quantities, and write it out first — it earns method marks on its own: v = f × λ.
3. Put the numbers in: v = 6 × 0.3.
4. Speed = 1.8 m/s — six wave-lengths of 0.3 m each sweep past every second, so the pattern as a whole covers 1.8 m in that same second.

That one relationship — speed, frequency and wavelength locked together — is the engine behind almost every calculation in this topic, from ripple tanks to echoes bouncing off a cliff to a hospital ultrasound scan. The full lesson below walks through why sound can't cross empty space, how to time an echo to measure distance, and how doctors use ultrasound to see inside the body — complete with an audio walkthrough and a worksheet to practise on.