What is a Wave?
A wave is a disturbance that travels through a medium (or space) carrying energy without transporting matter.
From ripples on water to the light reaching Earth from distant stars, waves are everywhere — in sound, light, radio signals, and even earthquakes.
Oscillations as the Source of Waves
A wave is a series of oscillations that travel.
Oscillation is a single object or system moving repeatedly back and forth around an equilibrium point. Examples include a swinging pendulum, a vibrating string, or a mass on a spring.
The oscillation of one particle (or field) causes the adjacent particles (or fields) to start their own oscillations. This creates a chain reaction that forms a propagating wave.
So, waves are travelling oscillations.
Example: Let’s take Sound Wave.
- When a person is speaking, it creates vibrations in their vocal cords—these are oscillations.
- These oscillations cause air molecules next to the vocal cords to move back and forth, creating a pressure wave.
- This process continues, with each air molecule oscillating and passing the energy to its neighbors, resulting in a sound wave that travels through the air to our ears.
Types of Waves
Waves can be grouped into different categories depending on their nature and the medium through which they propagate. Broadly, we classify them into:
- Mechanical Waves
- Electromagnetic Waves
- Matter Waves
Mechanical Waves
Mechanical waves require a material medium (like air, water, or a solid) to travel. They cannot travel in vacuum.
They are further classified based on how the particles of the medium move when the wave passes.
a) Transverse Waves
Particle Motion: Particles vibrate perpendicular to the direction of wave propagation.
Examples: Waves on a string, water surface waves.
b) Longitudinal Waves
Particle Motion: Particles vibrate parallel to the direction of wave propagation.
Examples: Sound waves in air, compression waves in a slinky.
Electromagnetic Waves
Electromagnetic (EM) waves do not require a medium—they can travel through vacuum.
They are produced by oscillating electric and magnetic fields.
EM waves are classified based on frequency or wavelength, forming the electromagnetic spectrum:
- Radio waves
- Microwaves
- Infrared (IR)
- Visible light
- Ultraviolet (UV)
- X-rays
- Gamma rays
Despite their differences in energy and wavelength, all EM waves travel at the speed of light in vacuum.
Matter Waves
Matter waves arise from the wave nature of moving particles, described by de Broglie’s relation:
where h is Planck’s constant and p is momentum.
Matter waves are not classified into types like mechanical or EM waves. Instead, any moving particle can exhibit wave-like behavior.
Examples:
- Electrons
- Protons
- Neutrons
- Atoms and molecules
Matter waves are important in quantum physics, electron diffraction, and particle behavior at small scales.
Basic Wave Parameters
| Quantity | Symbol | Unit | Description |
|---|---|---|---|
| Wavelength | λ | m | Distance between two consecutive crests or compressions |
| Frequency | f | Hz | Number of vibrations per second |
| Time Period | T | s | Time for one vibration  |
| Amplitude | A | m | Maximum displacement from mean position |
| Wave Speed | v | m/s | v = fλ |
The Wave Equation
The mathematical form of a traveling wave is:
y(x,t) = A sin (kx−ωt+ϕ)
where
- (wave number)
- ω = 2πf (angular frequency)
Wave Behaviors
Reflection, Refraction, and Diffraction
When waves travel through different surfaces or openings, they can change direction or behavior. This leads to phenomena such as reflection, refraction, and diffraction.
- Reflection: Wave bounces back from a boundary.
- Refraction: Change in direction when a wave passes into another medium.
- Diffraction: Bending of waves around obstacles or through slits.
Interference of Waves
When two or more waves meet, they combine according to the principle of superposition.
- Constructive Interference: Waves in phase → amplitudes add.
- Destructive Interference: Waves out of phase → amplitudes cancel.
Standing Waves
When identical waves travel in opposite directions, they form a standing wave — a pattern of nodes and antinodes.
In a stretched string:
n = 1, 2, 3, …
In air columns:
n = 1, 2, 3,…
Resonance in Waves
Resonance occurs when the frequency of the external force matches the natural frequency of the system — leading to a large amplitude of oscillation. See Oscillations – Resonance.
Example: Resonating air column in an organ pipe.
Applications of Waves
| Field | Application |
|---|---|
| Communication | Radio, TV, mobile, satellite transmission |
| Medicine | Ultrasound imaging, laser surgery |
| Navigation | SONAR and RADAR |
| Engineering | Vibration analysis, signal processing |
| Everyday life | Sound, music, light, heat |
Summary
- Waves are traveling disturbances that carry energy without transporting matter.
- They originate from oscillations of particles.
- Classified into mechanical, electromagnetic, and matter waves.
- Key characteristics include wavelength, frequency, amplitude, and speed.
- Phenomena like interference, diffraction, and standing waves explain many natural and technological effects.
Glossary of Key Terms
Recap of the Key Terms in Waves
Amplitude (A): The maximum displacement of a particle from its mean (rest) position.
Wavelength (λ): The distance between two consecutive crests, troughs, compressions, or rarefactions.
Frequency (f): The number of wave cycles produced per second; measured in hertz (Hz).
Time Period (T): The time taken to complete one full wave cycle.
Wave Speed (v): The speed at which the wave travels through a medium.
Transverse Wave: A wave where particles vibrate perpendicular to the direction of propagation.
Longitudinal Wave: A wave where particles vibrate parallel to the direction of propagation.
Mechanical Wave: A wave that requires a physical medium to travel (e.g., sound, water waves).
Electromagnetic Wave: A wave that does not require a medium; produced by oscillating electric and magnetic fields (e.g., light, radio waves).
Matter Wave: The wave associated with moving particles, described by de Broglie’s wavelength.
Reflection: The bouncing back of a wave when it hits a barrier.
Refraction: The bending of a wave when it moves from one medium to another.
Diffraction: The spreading or bending of a wave around obstacles or through openings.
Interference: The combination of two or more waves to form a new wave pattern (constructive or destructive).
Standing Wave: A wave pattern that stays in a fixed position, formed by the superposition of two waves moving in opposite directions.
Quiz
Recap the concepts you have learnt. Try to answer the questions. You can find the answer to any question by clicking on the icon.
What is a wave?
A wave is a disturbance that travels through a medium (or space) and carries energy without transporting matter.
What is the SI unit of frequency?
Hertz (Hz)
Define wavelength.
Wavelength (λ) is the distance between two consecutive crests, troughs, compressions, or rarefactions.
Write the formula for wave speed.
v = fλ
In a transverse wave, how do particles move?
Particles vibrate perpendicular to the direction of wave propagation.
Give two examples of transverse waves.
Waves on a string, electromagnetic waves.
In a longitudinal wave, how do particles move?
Particles vibrate parallel to the direction of wave propagation.
Name the regions of high and low pressure in a longitudinal wave.
- High pressure → Compression.
- Low pressure → Rarefaction.
What changes when a wave refracts?
The speed and direction of the wave change when entering another medium.
What is diffraction?
Diffraction is the bending or spreading of waves around obstacles or through openings.
What causes a wave to reflect?
A wave reflects when it hits a boundary or surface and bounces back.
Name two types of mechanical waves.
Transverse waves and longitudinal waves.
Do electromagnetic waves require a medium?
No. EM waves can travel through a vacuum.
List any three parts of the electromagnetic spectrum.
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays (any three of these).
What are matter waves?
Matter waves describe the wave nature of particles, given by de Broglie’s relation λ = h/p.
What is a standing wave?
A standing wave is a wave pattern that remains stationary, formed by the superposition of two waves moving in opposite directions.
What is interference?
Interference is the combination of two or more waves to produce a new resultant wave pattern.
What kind of interference increases amplitude?
Constructive interference.
What kind of interference reduces or cancels amplitude?
Destructive interference.