Waves - Definition, Types, Properties, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:40 PM IST

Introduction to waves

In physics, waves and vibrations are extremely important phenomena. Oscillations can be seen in many different forms throughout nature. We may easily discover vibration examples in practically every physical system, from massive oscillations of sea waves to the jiggling of atoms.

In physics, a wave is an oscillation or a disturbance that travels over time and space with an associated energy transfer. Wave motion often transfers energy from one point to another without causing permanent displacement of the medium's particles, resulting in negligible or minimal related mass transmission. Instead, they consist of oscillating or vibrating around a nearly fixed point.

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Introduction to waves
What is a wave? What is meant by wave or what is the meaning of wave and how are waves formed?
Types of waves
Properties of waves

Waves - Definition, Types, Properties, FAQs

What is a wave? What is meant by wave or what is the meaning of wave and how are waves formed?

Wave Definition and Wave meaning: A waves physics is a disturbance that propagates in a medium when the medium's particles cause neighbouring particles to move. They, in turn, cause others to move in the same way.

Waves come in a variety forms. During earthquakes, seismic waves shake the ground. We can see faraway stars because light waves move across the universe. Every sound we perceive is a wave as well.

To measure and describe all of these sorts of waves, scientists use a variety of qualities. The distance between one point on a wave and an identical point on the next, such as from crest to crest or trough to trough, is known as the wavelength.
The number of waves that travel through one place in one second is referred to as frequency. Frequency is measured in hertz.

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Periodic wave motion

The wave generated is known as a periodic wave if the disturbance is continuous and periodic in nature.
A sinusoidal periodic wave is a periodic wave that varies sinusoidally.
When a sinusoidal periodic wave passes through the medium, the particles perform simple harmonic motion (SHM).

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wave

Types of waves

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Waves come in a variety of forms, each with its own set of features. There are three categories based on particle motion orientation and energy direction:

Mechanical Waves
Electromagnetic Waves
Matter Waves

Mechanical waves

Mechanical waves are divided into two categories:

Longitudinal waves - In this form of the wave, the particle movement is parallel to the motion of the energy, i.e. the medium displacement is in the same direction as the wave. Sound waves and pressure waves are two examples.
Transverse waves - occur when the motion of the particles is at right angles or perpendicular to the motion of the energy. Light is an example of a transverse wave.

Electromagnetic waves

There is no requirement for the presence of any medium for the propagation of electromagnetic waves. In other words, electromagnetic waves travel at the same speed from one place to another in a vacuum. Periodic variations in magnetic fields occur in these waves, which are referred to as electromagnetic waves.

The interaction of magnetic and electric fields produces electromagnetic waves. Electromagnetic waves are responsible for the light and colour that you see. Microwaves, light waves, heat radiation, X-rays, radio waves, and ultraviolet waves are all examples of electromagnetic waves.

Matter waves

De Broglie waves are another name for matter waves. A beam of electrons, according to Louis de Broglie's hypothesis, can be deflected like any other ray of water wave or electromagnetic radiation.

These waves have properties that are analogous to those of matter, such as atoms and molecules. De Broglie's equation, which represents the "dual" nature of matter, is represented by a number of equations. Matter waves have a frequency that is proportional to their kinetic energy.

Based on the transfer of energy

Standing Waves
Progressive Waves

Standing waves are restricted to a region with no energy or momentum transfer, whereas progressive waves transfer energy and momentum between the medium's particles.

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Properties of waves

The organised transmission of disturbance from one place to another is referred to as a wave. Mechanical and non-mechanical waves are both possible. Mechanical waves, like sound waves, must propagate via a medium. Electromagnetic waves, on the other hand, are non-mechanical waves that do not require a medium to travel and can even go into space.

Transverse waves occur when the particles of the medium move in a direction that is perpendicular to the wave propagation. Longitudinal waves are waves in which the medium's particles vibrate in a direction parallel to the wave's propagation direction.

wave amplitude

Amplitude

The amplitude of a wave is defined as its maximum displacement from its mean position. The maximum height is measured from the centre line to the crest or trough. The crest of the wave is the highest point, and the trough is the lowest point. The amplitude of a wave is measured in metres.

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Frequency

The frequency is defined as the number of vibrations travelling through a fixed point in a given amount of time. The frequency unit is Hertz.

Time period

The time it takes for a whole wave to pass through a particular point is referred to as the time period. The duration is expressed in seconds. The reciprocal of the frequency is the time period.

Speed

A wave's speed is defined as the distance travelled by a certain point on the wave in a given time interval. The speed of a wave is measured in metres per second.

Phase or phase angle (φ)

It denotes the state of vibration of a medium particle in relation to its mean position.

Phase difference (δφ)

It denotes a particle's various vibrational states at two different times (or any pair of particles at the same time).

ΔΦ = Φ2 – Φ1

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NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. What are the different types of waves?

Based on the orientation of particle and energy the waves are classified as

Mechanical Waves
Electromagnetic Waves
Matter Waves

2. Give some examples of transverse waves?

The examples of transverse waves are:

Torsion Waves
Stringed instruments
Light Waves
Water Waves(ripples of gravity waves)

3. Name the parts of a longitudinal wave?

There are two parts to the longitudinal wave. They are the compression (where the particles come together) and rarefaction (where the particles are apart).

4. What are the examples of longitudinal waves?

Sound waves, compression waves and p-type earthquake waves are some of the examples of longitudinal waves.

5. What is a wavelength?

The distance between two identical points (adjacent crests or troughs) is measured in wavelength. Its length is measured in metres. The wavelength and the frequency are inversely proportional.

6. How do shock waves differ from regular waves?

Shock waves are a type of propagating disturbance characterized by an abrupt, nearly discontinuous change in pressure, temperature, and density of the medium. Unlike regular waves, shock waves travel faster than the speed of sound in the medium and can cause sudden, dramatic changes in the medium's properties.

7. What is the significance of the wave function in quantum mechanics?

The wave function is a fundamental concept in quantum mechanics that describes the quantum state of a particle or system. It provides information about all possible measurements of a system's properties. The square of the wave function's magnitude gives the probability density of finding a particle at a specific point in space and time.

8. How do seismic waves provide information about Earth's interior?

Seismic waves, generated by earthquakes or artificial explosions, travel through Earth's interior at different speeds depending on the properties of the materials they pass through. By studying how these waves propagate and reflect off different layers, scientists can infer information about Earth's internal structure, composition, and properties.

9. What is the difference between group velocity and phase velocity?

Group velocity is the velocity at which the overall shape of a wave's amplitudes propagates through space. Phase velocity is the velocity at which the phase of any one frequency component of the wave travels. In dispersive media, where different frequencies travel at different speeds, group velocity and phase velocity can differ.

10. What is wave attenuation?

Wave attenuation is the gradual loss of wave intensity as it propagates through a medium. This can be due to factors like absorption of energy by the medium, scattering, or spreading of the wave. Attenuation is important in many practical applications, such as signal transmission in communications or the propagation of seismic waves through Earth.

11. How do waves transfer energy without transferring matter?

Waves transfer energy through the oscillation or vibration of particles in the medium. Each particle transfers energy to its neighboring particles, creating a chain reaction that propagates the wave. The particles themselves don't move along with the wave; they only vibrate around their equilibrium positions.

12. What is wavelength, and how is it measured?

Wavelength is the distance between two consecutive crests or troughs in a wave. It is typically measured in meters (m) and represents the spatial period of the wave. To measure wavelength, you can use the distance between two adjacent peaks or troughs of the wave.

13. How are frequency and wavelength related in a wave?

Frequency and wavelength are inversely related in a wave. As frequency increases, wavelength decreases, and vice versa. This relationship is described by the wave equation: v = fλ, where v is the wave speed, f is the frequency, and λ is the wavelength.

14. What is the amplitude of a wave?

The amplitude of a wave is the maximum displacement of a particle from its equilibrium position. In a transverse wave, it's the height of a crest or depth of a trough from the rest position. Amplitude is related to the energy carried by the wave – higher amplitude means more energy.

15. How does the speed of a wave depend on the medium it's traveling through?

The speed of a wave depends on the properties of the medium it's traveling through. For mechanical waves, factors like density and elasticity of the medium affect wave speed. In general, waves travel faster through stiffer or more rigid mediums. For example, sound travels faster in water than in air.

16. What are the two main types of waves?

The two main types of waves are mechanical waves and electromagnetic waves. Mechanical waves require a medium to propagate (e.g., sound waves in air or water waves in a lake), while electromagnetic waves can travel through a vacuum (e.g., light waves or radio waves).

17. Can you explain the difference between transverse and longitudinal waves?

Transverse waves have particle displacements perpendicular to the direction of wave propagation (e.g., waves on a string). Longitudinal waves have particle displacements parallel to the direction of wave propagation (e.g., sound waves in air). The key difference is in the direction of particle oscillation relative to the wave's travel direction.

18. How do electromagnetic waves differ from mechanical waves?

Electromagnetic waves don't require a medium to propagate and can travel through a vacuum, while mechanical waves need a medium. Electromagnetic waves are created by oscillating electric and magnetic fields, while mechanical waves involve the oscillation of particles in a medium. All electromagnetic waves travel at the speed of light in a vacuum.

19. What is a standing wave?

A standing wave is a stationary wave pattern formed by the interference of two waves of the same frequency traveling in opposite directions. Unlike traveling waves, standing waves don't propagate energy through space. They have fixed points called nodes (no displacement) and antinodes (maximum displacement).

20. What is wave interference?

Wave interference occurs when two or more waves meet and combine. The resulting wave is the sum of the individual waves' displacements at each point. Interference can be constructive (waves reinforce each other) or destructive (waves cancel each other out), depending on how the waves align.

21. What is a wave in physics?

A wave is a disturbance that propagates through a medium, transferring energy from one point to another without the transfer of matter. Waves can occur in various forms, such as mechanical waves (like sound or water waves) or electromagnetic waves (like light).

22. What is resonance in the context of waves?

Resonance is the tendency of a system to oscillate with greater amplitude at certain frequencies, called resonant frequencies. It occurs when a system is able to store and easily transfer energy between different forms. In waves, resonance can lead to standing waves and is important in many applications, from musical instruments to radio tuning.

23. How do tsunamis differ from regular ocean waves?

Tsunamis are long-wavelength waves caused by large-scale disturbances like earthquakes or landslides, while regular ocean waves are typically caused by wind. Tsunamis have much longer wavelengths and periods than wind-generated waves. In deep water, tsunamis may be barely noticeable, but they can grow to enormous heights in shallow coastal areas.

24. What is the relationship between wave speed, frequency, and wavelength?

The relationship is described by the wave equation: v = fλ, where v is wave speed, f is frequency, and λ is wavelength. This equation shows that for a given wave speed, as frequency increases, wavelength must decrease proportionally, and vice versa.

25. How do sound waves travel through different mediums?

Sound waves are longitudinal waves that travel through the compression and rarefaction of particles in a medium. They travel faster in denser mediums (like solids) compared to less dense mediums (like gases). The speed of sound also depends on the elasticity of the medium.

26. What is the photoelectric effect, and how does it relate to wave-particle duality?

The photoelectric effect is the emission of electrons from a material when light shines on it. It demonstrates the particle nature of light, as the effect depends on the frequency (energy) of the light, not its intensity. This phenomenon, explained by Einstein, was crucial in developing the concept of wave-particle duality and quantum mechanics.

27. What is the concept of wave function collapse in quantum mechanics?

Wave function collapse is the phenomenon where a quantum system ceases to exist as a superposition of states and becomes a single eigenstate when a measurement is made. Before measurement, the system is described by a wave function representing all possible states. Upon measurement, this wave function is said to "collapse" into a definite state. This concept is central to the Copenhagen interpretation of quantum mechanics and relates to the observer effect in quantum systems.

28. What is the relationship between waves and the concept of quantum entanglement?

Quantum entanglement is a phenomenon where two or more particles become correlated in such a way that the quantum state of each particle cannot be described independently. This is often explained using wave functions. When particles are entangled, their wave functions become inseparable, meaning that measuring one particle instantaneously affects the state of the other, regardless of the distance between them. This "spooky action at a distance," as Einstein called it, is a consequence of the wave nature of quantum particles and the superposition principle.

29. Can you explain the concept of wave superposition?

Wave superposition is the principle that when two or more waves overlap, the resulting displacement at any point is the sum of the displacements of the individual waves at that point. This principle applies to all types of waves and is the basis for understanding wave interference patterns.

30. How do reflection and refraction differ for waves?

Reflection occurs when a wave bounces off a boundary between two media, changing direction but staying in the original medium. Refraction occurs when a wave passes from one medium to another, changing its speed and direction. Both phenomena are governed by specific laws (e.g., law of reflection, Snell's law for refraction).

31. What is wave diffraction?

Diffraction is the bending of waves around obstacles or through openings. It's most noticeable when the size of the obstacle or opening is comparable to the wavelength of the wave. Diffraction explains how waves can "spread out" after passing through a small opening or around a corner.

32. How does the Doppler effect work for waves?

The Doppler effect is the change in frequency of a wave for an observer moving relative to its source. When the source and observer move closer, the observed frequency increases (wavelength decreases). When they move apart, the observed frequency decreases (wavelength increases). This effect applies to both sound and light waves.

33. What is wave polarization?

Polarization is a property specific to transverse waves, particularly electromagnetic waves. It describes the orientation of the wave's oscillations. For example, in linearly polarized light, the electric field oscillates in a single plane perpendicular to the direction of propagation. Polarization is important in many optical applications and technologies.

34. How does the energy of a wave relate to its amplitude and frequency?

The energy of a wave is proportional to the square of its amplitude. This means doubling the amplitude quadruples the energy. For electromagnetic waves, energy is also directly proportional to frequency. Higher frequency waves (like X-rays) carry more energy than lower frequency waves (like radio waves).

35. What is wave dispersion?

Wave dispersion occurs when different frequencies of a wave travel at different speeds through a medium. This causes the wave to spread out or separate into its component frequencies. Dispersion is responsible for phenomena like the separation of white light into colors by a prism or the formation of rainbows.

36. What is the principle of wave-particle duality?

Wave-particle duality is a concept in quantum mechanics stating that every particle or quantum entity can be described as either a particle or a wave. It suggests that the behavior of matter and light has characteristics of both waves and particles, depending on the circumstances of the experiment.

37. How do waves behave at the boundary between two different mediums?

When a wave encounters a boundary between two mediums, part of the wave may be reflected back into the original medium, while part may be transmitted (refracted) into the new medium. The behavior depends on the properties of both mediums and can involve changes in speed, direction, and sometimes the type of wave (e.g., longitudinal to transverse).

38. How do standing waves form in musical instruments?

Standing waves in musical instruments form when waves reflecting from the ends of the instrument interfere with incoming waves. This creates a pattern of nodes (points of no displacement) and antinodes (points of maximum displacement). The frequencies at which standing waves can form depend on the instrument's size and shape, determining the notes it can produce.

39. How do gravitational waves differ from other types of waves?

Gravitational waves are ripples in the curvature of spacetime caused by accelerating masses, as predicted by Einstein's theory of general relativity. Unlike electromagnetic or mechanical waves, they don't propagate through a medium but through spacetime itself. They are extremely weak and were only directly detected for the first time in 2015.

40. What is the principle behind noise-cancelling headphones?

Noise-cancelling headphones use the principle of destructive interference. They detect ambient noise with a microphone and generate sound waves that are exactly out of phase with the noise. When these generated waves combine with the ambient noise, they cancel each other out, reducing the perceived noise level.

41. How do waves contribute to the greenhouse effect?

The greenhouse effect involves the absorption and emission of electromagnetic waves, particularly infrared radiation. Greenhouse gases in the atmosphere absorb infrared radiation emitted by Earth's surface. They then re-emit this energy in all directions, including back towards the surface, leading to warming. This process involves the interaction of waves with matter.

42. What is the concept of wave packets in quantum mechanics?

A wave packet is a localized wave disturbance that results from the superposition of waves of different wavelengths. In quantum mechanics, wave packets are used to describe the behavior of particles, representing a compromise between the wave-like and particle-like properties of matter. The shape and spread of a wave packet can provide information about a particle's position and momentum.

43. How do waves behave in a double-slit experiment?

In a double-slit experiment, waves passing through two narrow slits create an interference pattern on a screen behind the slits. This pattern, consisting of bright and dark bands, results from the constructive and destructive interference of waves from the two slits. This experiment demonstrates the wave nature of light and matter and is fundamental to understanding quantum mechanics.

44. What is the relationship between waves and the uncertainty principle?

The uncertainty principle, formulated by Heisenberg, is closely related to the wave nature of particles. It states that certain pairs of physical properties, like position and momentum, cannot be simultaneously measured with arbitrary precision. This principle arises from the wave-like nature of matter and the mathematical properties of waves, particularly the Fourier transform relationship between position and momentum representations.

45. How do waves play a role in the functioning of MRI machines?

MRI (Magnetic Resonance Imaging) machines use radio waves and strong magnetic fields to create detailed images of the body. The machine applies radio frequency waves to hydrogen atoms in the body, causing them to resonate and emit signals. These signals are then detected and processed to create images. The whole process relies on the principles of wave resonance and the wave nature of electromagnetic radiation.

46. What is the significance of the wave equation in physics?

The wave equation is a fundamental equation in physics that describes the propagation of waves. It's a second-order partial differential equation that relates the curvature of a wave in space to its acceleration in time. This equation is crucial in many areas of physics, including acoustics, electromagnetics, and quantum mechanics, as it describes how waves of various types behave and propagate.

47. How do waves contribute to the phenomenon of quantum tunneling?

Quantum tunneling is a phenomenon where particles can pass through a potential barrier that they classically shouldn't be able to overcome. This is explained by the wave nature of particles in quantum mechanics. The wave function of a particle doesn't abruptly go to zero at a barrier but decays exponentially inside it. If the barrier is thin enough, there's a non-zero probability of finding the particle on the other side, effectively "tunneling" through the barrier.

48. How do waves explain the phenomenon of diffraction gratings?

Diffraction gratings are optical components with a periodic structure that split and diffract light into several beams traveling in different directions. The principle behind this is wave interference. When light waves encounter the grating's regularly spaced lines or grooves, they diffract. The diffracted waves interfere constructively at certain angles, creating bright spots or lines. The pattern produced depends on the wavelength of the light and the spacing of the grating, allowing diffraction gratings to be used for spectral analysis.

49. How do waves contribute to the functioning of fiber optic communication?

Fiber optic communication relies on the wave nature of light. Information is transmitted as pulses of light (electromagnetic waves) through thin fibers of glass or plastic. These waves undergo total internal reflection within the fiber, allowing them to travel long distances with minimal loss. The wave properties of light, such as its frequency and phase, can be modulated to encode information. Additionally, the wave nature allows for phenomena like dispersion and nonlinear effects, which are important considerations in designing and optimizing fiber optic systems.

50. What is the concept of wave-particle duality in the context of the delayed choice quantum eraser experiment?

The delayed choice quantum eraser experiment is a complex setup that demonstrates the wave-particle duality of light in a striking way. It shows that the act of measuring or observing a quantum system can determine whether light behaves as a wave or a particle, even after the light has already passed through the experimental apparatus. This experiment highlights how the wave and particle natures of light are complementary aspects of quantum entities, and that our choice of measurement can influence how we perceive these aspects, even seemingly retroactively.

51. How do waves explain the phenomenon of optical beating?

Optical beating occurs when two light waves of slightly different frequencies interfere. The resulting wave shows a periodic variation in intensity, with the beat frequency equal to the difference between the two original frequencies. This phenomenon is a direct consequence of wave superposition and interference. Optical beating is used in various applications, including laser frequency stabilization and high-precision spectroscopy.