Waves
A disturbance that transfers energy from place to place without transferring matter.
A. Types of Waves
Wave Classification
| Type | Description | Examples |
|---|---|---|
| Transverse Wave | Particles vibrate perpendicular to direction of wave travel | Light, water waves, electromagnetic waves |
| Longitudinal Wave | Particles vibrate parallel to direction of wave travel | Sound waves, compression waves |
| Mechanical Wave | Requires a medium to travel | Sound, water waves, seismic waves |
| Electromagnetic Wave | Does NOT require a medium — travels in vacuum | Light, X-rays, radio waves, gamma rays |
B. Wave Properties & Terminology
Key Wave Terms
| Term | Definition | Unit |
|---|---|---|
| Amplitude (A) | Maximum displacement from equilibrium position | metres (m) |
| Wavelength (λ) | Distance between two successive crests or troughs | metres (m) |
| Frequency (f) | Number of complete waves per second | Hertz (Hz) |
| Period (T) | Time for one complete wave cycle | seconds (s) |
| Wave Speed (v) | Distance traveled per unit time | m/s |
Wave Speed
v = f × λ
wave speed = frequency × wavelength
Period
T = 1 / f
Period is the reciprocal of frequency
C. Standing (Stationary) Waves
Standing Waves
- Formed when two identical waves travel in opposite directions and superpose
- Have nodes (zero displacement) and antinodes (maximum displacement)
- Distance between two consecutive nodes = λ/2
- Produced in musical instruments — strings, organ pipes
- The wave pattern appears to stand still (does not travel)
D. Sound Waves
Properties of Sound
- Sound is a mechanical, longitudinal wave — requires a medium
- Speed of sound in air at 20°C ≈ 343 m/s
- Speed order: solid > liquid > gas
- Pitch: determined by frequency — high frequency = high pitch
- Loudness: determined by amplitude — large amplitude = louder sound
- Ultrasound: frequency > 20,000 Hz — used in medical imaging (sonography)
- Infrasound: frequency < 20 Hz — used by elephants and whales
⚡ MCQ Tip
v = fλ. T = 1/f. Sound travels fastest in solids. Transverse = perpendicular vibration.
Longitudinal = parallel. Gamma rays have highest frequency. Radio waves have lowest.
E. Electromagnetic Spectrum
EM Spectrum — Increasing Frequency →
All EM waves travel at c = 3 × 10⁸ m/s in vacuum
Radio Waves
Lowest frequency
Broadcasting, communication
Microwaves
~10⁹ – 10¹² Hz
Cooking, radar, satellite
Infrared
~10¹² – 10¹⁴ Hz
Heat lamps, remote controls, night vision
Visible Light
~10¹⁴ Hz
Sight, photography
Ultraviolet (UV)
~10¹⁵ Hz
Sterilisation, detecting forged notes
X-Rays
~10¹⁷ – 10¹⁹ Hz
Medical imaging, security scanners
Gamma Rays
Highest frequency
Cancer treatment, sterilising medical equipment
Live Animation: Transverse Wave Propagation
Transverse Wave — Particle Motion Tracer
The coloured dot shows a single particle's vertical oscillation
Quick MCQ Revision
| Formula / Fact | Meaning |
|---|---|
| v = fλ | Wave speed = frequency × wavelength |
| T = 1/f | Period = 1 ÷ frequency (seconds) |
| Transverse wave | Particle vibration ⊥ to wave direction (light, water) |
| Longitudinal wave | Particle vibration ∥ to wave direction (sound) |
| Sound speed (air) | 343 m/s at 20°C |
| Speed order | Solid > Liquid > Gas |
| Ultrasound | f > 20,000 Hz — medical imaging |
| Infrasound | f < 20 Hz — elephants, whales |
| Gamma rays | Highest frequency in EM spectrum |
| Radio waves | Lowest frequency in EM spectrum |
| EM speed (vacuum) | c = 3 × 10⁸ m/s (all EM waves) |
| Standing wave nodes | Distance between 2 nodes = λ/2 |