Quick Overview
- Waves transfer energy through oscillations without moving the medium itself
- Key properties: amplitude, wavelength, frequency, and wave speed — all connected by v = f × λ
- Two types: transverse (oscillation perpendicular to wave travel) and longitudinal (oscillation parallel to wave travel)
- Wave behaviour: reflection, refraction (speed + direction change), and diffraction (spreading through gaps)
- Ripple tanks let us see and measure these properties in water waves
1. Features of Waves
1.1 Waves Transfer Energy, Not Matter
This is the most important thing to understand about waves. A wave is a pattern of energy traveling through a medium, not the medium itself moving along.
💡 Think of it this way
Watch a duck floating on the ocean. When a wave passes underneath, the duck bobs up and down, but it doesn't move across the water with the wave. The duck stays in roughly the same place. This proves the water particles don't travel with the wave — only the energy does.
Sound waves work the same way. When a speaker plays music, the air molecules vibrate back and forth around their fixed positions. They don't travel from the speaker to your ear. The wave pattern does.
What this means:
- Waves = energy transfer + oscillations at fixed points
- The pattern (wave) moves; the particles stay local
- Frequency stays constant as the wave travels (unless it enters a new medium)
1.2 Wave Motion: How Waves Are Created
Waves can be demonstrated in three main ways:
Vibrations in ropes and springs: Shake one end of a rope quickly — the disturbance travels along it as a wave. Each part of the rope vibrates perpendicular to the rope's length.
Experiments with water waves: A ripple tank contains shallow water. A motor vibrates a paddle, creating circular or straight-line wavefronts that spread across the surface.
Key insight: In all cases, the particles oscillate about a fixed equilibrium position. The wave is the organized pattern of these oscillations.
1.3 Features of a Wave — Definitions & Measurements
⚠️ Common Mistake
Students often mix up "the wave" with "the particle motion." Remember: the wave causes particles to move, but particles are not the wave itself.
Amplitude (A)
Definition: The maximum displacement of a particle from its undisturbed position.
Measured in: metres (m)
In plain words: How far up (or to the side) a particle moves away from where it would sit if there was no wave.
Undisturbed position ─────────
╱╲
A → ╱ ╲
╱ ╲
╱ ╲ ← Amplitude = A
╲
On a graph: Measure vertically from the center line (undisturbed position) to the peak or trough. Both distances equal A.
Wavelength (λ)
Definition: The distance from one point on the wave to the next identical point on the following wave.
Measured in: metres (m) | Symbol: λ (lambda)
Frequency (f)
Definition: