Amplitude
Amplitude is the maximum displacement of a wave from its equilibrium (rest) position, representing the "height" of a wave. It is denoted by A and measured in metres for mechanical waves, or in volts, pascals, or other units depending on context. Amplitude is directly related to the energy carried by the wave: the greater the amplitude, the greater the energy, which is why louder sounds and brighter lights have larger amplitudes.
Key Formula
E is proportional to A squared
LaTeX: E \propto A^2
| Symbol | Meaning | Unit |
|---|---|---|
| E | Energy of the wave | J |
| A | Amplitude | m |
Worked Example
Problem
Wave X has an amplitude of 2 m and Wave Y has an amplitude of 4 m. How many times more energy does Wave Y carry compared to Wave X?
Solution
Step 1: Energy ∝ A². Step 2: E_Y / E_X = (A_Y)² / (A_X)² = (4)² / (2)² = 16 / 4. Step 3: E_Y / E_X = 4.
Answer
Wave Y carries 4 times more energy than Wave X.
Amplitude and Its Effect on Wave Properties
| Wave Type | Amplitude Measure | Unit | Effect of Larger Amplitude |
|---|---|---|---|
| Sound | Pressure variation | Pa | Louder sound |
| Water wave | Surface displacement | m | Bigger waves, more energy |
| Light | Electric field strength | V/m | Brighter light |
| Seismic wave | Ground displacement | m | Greater earthquake magnitude |
| AC current | Peak current | A | More power delivered |
Interactive Tools
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Related Terms
Wave
A wave is a disturbance that transfers energy through a medium or through space without permanently displacing the medium itself. Waves are fundamental to how energy propagates in nature, from ocean ripples to light traveling across the universe. They are characterised by properties such as wavelength, frequency, amplitude, and speed, and underpin technologies ranging from radio communication to medical ultrasound.
Frequency
Frequency is the number of complete wave cycles that pass a fixed point per unit time, measured in hertz (Hz), where 1 Hz equals one cycle per second. It determines the pitch of a sound (higher frequency = higher pitch) and the colour of light (higher frequency = more energetic, bluer light). Frequency is inversely proportional to the wave period: f = 1/T.
Wavelength
Wavelength is the spatial distance between two consecutive points that are in the same phase of a wave, such as crest to crest or trough to trough. It is denoted by the Greek letter lambda (λ) and measured in metres. Wavelength is inversely related to frequency: higher-frequency waves have shorter wavelengths, which is why X-rays (short λ) are more energetic than radio waves (long λ).
From Latin "amplitudo" (breadth, width), from "amplus" (large, spacious). Adopted in physics in the 19th century to describe the magnitude of wave displacement.