General Wave Properties
Waves are disturbances that transfer energy from one point to another. They are produced by vibrating sources such as a rope, spring, or oscillating paddle in water.
Key Ideas
- Waves transmit energy — not material particles.
- Examples: water ripples, sound waves, light, and radio waves.
- Waves can be transverse or longitudinal.
Basic Quantities
| Term | Meaning | Example / Note |
|---|---|---|
| Amplitude | Height of a crest or depth of a trough from the mid-position. | Larger amplitude → louder sound / brighter light. |
| Wavelength (λ) | One complete wave cycle length; determines the wave’s spatial size. | Measured in metres (m); for sound, λ ≈ 0.03 m in air. |
| Frequency (f) | How many waves pass a point each second (Hz). | f = 1 / T (where T = period in seconds). |
| Wave Speed (v) | Distance travelled by a crest or trough each second. | v = f × λ |
Wave Equation
v = f × λ where v = speed (m s⁻¹), f = frequency (Hz), λ = wavelength (m).
Example: If v = 3.0 × 10⁸ m/s and f = 2.4 × 10⁹ Hz, then λ ≈ 0.125 m.
Wave Types
- Transverse wave: particle motion ⟂ to wave direction (e.g., light, water ripples).
- Longitudinal wave: particle motion ∥ to wave direction (e.g., sound).
- Longitudinal waves show compressions (high pressure) and rarefactions (low pressure).
Wave Behaviour at Boundaries
- Reflection — wave bounces back; speed, frequency, wavelength unchanged; direction changes.
- Refraction — wave bends when speed changes crossing media; frequency constant, wavelength changes.
- Diffraction — wave spreads after a gap or obstacle; most when gap ≈ λ.
Wavelength in Practice
Shorter wavelengths → higher frequency → more energy (e.g., UV > visible > IR). Longer wavelengths (e.g., radio) spread more by diffraction.
Exam Tips
- Label λ between two crests (or compressions) on diagrams.
- During refraction: speed ↓ → λ ↓ → wave bends towards normal.
- Use the correct units: λ in m, f in Hz, v in m/s.
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