General Properties of WavesCopy
Cheat Sheet: General Properties of Waves (O Level / IGCSE Physics)
1. Energy Transfer in Waves
- Waves transfer energy from one place to another without transferring matter
- Particles vibrate around fixed positions (no net movement of particles)
2. Wave Motion Illustration
- Rope or spring experiment: moving one end up and down creates transverse wave
- Water ripple tank: shows circular spreading of waves from a source
3. Wave Features
| Feature | Description |
|---|---|
| Wavefront | Line joining points vibrating in phase (e.g. all crests) |
| Crest (peak) | Highest point of a wave |
| Trough | Lowest point of a wave |
| Wavelength (λ) | Distance between two consecutive crests/troughs |
| Amplitude | Maximum displacement from the rest position |
| Frequency (f) | Number of complete waves passing a point per second |
| Wave speed (v) | Speed at which wave travels through medium |
4. Key Definitions
- (a) Frequency (f):
Number of wavelengths passing a fixed point per second
Unit: Hertz (Hz) - (b) Wavelength (λ):
Distance between two identical points on consecutive waves (e.g. crest to crest)
Unit: metre (m) - (c) Amplitude:
Maximum distance a particle moves from its undisturbed (mean) position
5. Wave Speed Equation
- v = f × λ
where:
v = wave speed (m/s)
f = frequency (Hz)
λ = wavelength (m)
6. Transverse Waves
- Vibrations are perpendicular to energy transfer direction
- Examples:
- Electromagnetic waves (light, radio)
- Water surface waves
- Seismic S-waves
7. Longitudinal Waves
- Vibrations are parallel to energy transfer direction
- Examples:
- Sound waves
- Seismic P-waves
- Consist of compressions (particles close together) and rarefactions (particles spread out)
8. Wave Behaviours
(a) Reflection
- Wave bounces off a surface
- Angle of incidence = angle of reflection
(b) Refraction
- Wave changes speed and direction at boundary between two mediums
- If speed decreases → bends towards normal
- If speed increases → bends away from normal
(c) Diffraction
- Wave spreads out when passing through a gap or around an obstacle
- More noticeable when wavelength ≈ gap size
9. Diffraction Through a Gap
- Narrow gap (≈ wavelength) → strong spreading (wide diffraction)
- Wide gap (≫ wavelength) → weak spreading (small diffraction)
10. Ripple Tank Demonstrations (Using Water Waves)
(a) Reflection:
- Place a flat barrier; observe waves bouncing back at equal angle
(b) Refraction:
- Use a deep and shallow region (glass or plastic sheet under part of tank)
- Waves slow down and change direction when entering shallower region
(c) Diffraction Through a Gap:
- Use two narrow barriers with a gap between
- Observe spreading of waves after they pass through
(d) Diffraction Around an Edge:
- Place one obstacle in path of wavefront
- Observe bending/spreading of wave around the object
11. Wavelength and Diffraction at an Edge
- Longer wavelengths diffract more around edges
- Shorter wavelengths diffract less and cast sharper shadows