General properties of waves Revision Notes

A wave is a disturbance or oscillation that travels through space or a medium, transferring energy from one point to another without the net movement of matter. Waves can be mechanical, requiring a medium (such as air, water, or solids), or electromagnetic, which can travel through a vacuum.

The key characteristic of a wave is that it carries energy through the oscillation of particles or fields, not by transporting the particles themselves over long distances. Instead, particles vibrate or oscillate around fixed equilibrium positions as the wave passes.

• Waves transfer energy, not matter.
• Particles oscillate about fixed points.
• Energy moves through the medium or space.

When a wave passes through a medium, the particles of the medium move temporarily from their rest positions but return after the wave has passed. This oscillatory motion allows energy to be passed along the medium without the particles themselves travelling with the wave.

For example, in water waves, water molecules move in circular or vertical oscillations but do not travel horizontally with the wave. Similarly, in sound waves, air particles vibrate back and forth along the direction of wave travel but do not move forward with the wave.

This principle ensures that energy can be transmitted efficiently over distances without the physical displacement of the medium.

• Particles oscillate locally, not transported.
• Energy propagates through successive particle vibrations.
• Medium returns to original position after wave passes.

Mechanical waves such as sound waves, water waves, and seismic waves require a medium to travel through and transfer energy by particle oscillations.

Electromagnetic waves, including light, radio waves, and X-rays, transfer energy through oscillating electric and magnetic fields and do not require a medium.

In all these cases, the energy carried by the wave can do work, such as causing a detector to vibrate or heating an object, without the medium itself moving from the source to the receiver.

• Sound waves: air particles vibrate, energy moves forward.
• Water waves: water molecules oscillate, energy travels across surface.
• Electromagnetic waves: energy transferred by fields, no medium needed.

Energy transfer in waves occurs through the oscillation of particles or fields. In mechanical waves, particles are displaced from equilibrium positions and exert forces on neighbouring particles, causing them to oscillate and pass energy along.

The energy carried by a wave is proportional to the square of its amplitude; larger amplitude waves carry more energy.

The speed of energy transfer depends on the wave speed, which is determined by the properties of the medium (for mechanical waves) or the nature of the wave (for electromagnetic waves).

• Energy transfer via particle oscillations and interactions.
• Energy ∝ amplitude².
• Wave speed depends on medium properties.

To draw a diagram showing this concept: 1. Draw a horizontal line representing the medium at rest (equilibrium position). 2. Above this line, sketch a wave pulse or sinusoidal wave moving from left to right. 3. Mark a particle of the medium at a fixed horizontal position. 4. Show the particle oscillating vertically (for transverse waves) or horizontally (for longitudinal waves) about its equilibrium position as the wave passes.

Label the particle's oscillation and indicate that it returns to its original position after the wave passes, while the wave pulse moves forward, carrying energy.

• Draw medium's equilibrium line.
• Sketch wave pulse moving right.
• Show particle oscillating about fixed point.
• Label energy transfer direction and particle motion.

Wave motion is the transfer of energy through a medium caused by a disturbance or vibration, without the permanent displacement of the particles of the medium. The particles oscillate about their fixed positions, passing energy from one to the next.

In wave motion, energy travels through the medium, but the medium itself does not move along with the wave. This is a key characteristic distinguishing waves from the movement of matter.

Examples of wave motion include vibrations in ropes and springs, and waves on the surface of water. These examples help visualise how energy is transmitted through different media.

• Wave motion transfers energy without permanent displacement of the medium.
• Particles of the medium oscillate about fixed positions.
• Energy is passed from particle to particle along the medium.

When a rope or spring is disturbed by a vibration, waves travel along its length. These waves can be transverse or longitudinal depending on the direction of particle vibration relative to the wave direction.

In a transverse wave, particles vibrate perpendicular to the direction of wave travel. For example, when you flick a rope up and down, the wave moves horizontally while the rope moves vertically.

In a longitudinal wave, particles vibrate parallel to the direction of wave travel. Compressing and releasing a spring along its length produces longitudinal waves, where coils move back and forth along the spring's length.

• Transverse waves: particle vibration is perpendicular to wave direction (e.g., rope vibrations).
• Longitudinal waves: particle vibration is parallel to wave direction (e.g., spring vibrations).
• Energy is transmitted along the rope or spring by these vibrations.

Water waves are an example of wave motion on the surface of a liquid. When a disturbance occurs, such as dropping a stone into water, ripples spread out from the point of disturbance.

Water waves are transverse in nature at the surface, where water particles move roughly up and down while the wave travels horizontally. However, water particles also move in circular orbits beneath the surface, combining transverse and longitudinal motions.

These waves transfer energy across the water surface without transporting water itself over large distances.

• Water waves are surface waves with particles moving in circular paths.
• Energy moves outward as ripples from the disturbance point.
• Water particles oscillate but do not travel with the wave.

Simple experiments can demonstrate wave motion in ropes, springs, and water. These help visualise how energy is transferred through vibrations.

Apparatus for rope waves includes a long rope fixed at one end and a hand to create vibrations at the other. For springs, a helical spring fixed at one end can be compressed and released to produce longitudinal waves.

For water waves, a ripple tank or a shallow tray of water can be used. Disturbing the water surface with a finger or a vibrating source creates visible waves spreading outwards.

• Rope wave experiment: fix one end, create transverse vibrations at the other; observe wave travel.
• Spring wave experiment: compress and release coils to create longitudinal waves.
• Water wave experiment: disturb water surface and observe ripples spreading.
• Variables include frequency and amplitude of vibrations, wave speed, and wavelength.
• Repeat measurements to improve accuracy and reduce uncertainty.
• Safety: ensure no slipping hazards from water spills and handle apparatus carefully.

Wave motion involves energy transfer through oscillations of particles in a medium without net movement of the medium itself.

Transverse waves have particle vibrations perpendicular to wave direction; longitudinal waves have vibrations parallel to wave direction.

Practical examples such as ropes, springs, and water waves illustrate these principles clearly and allow measurement of wave properties in experiments.

• Energy transfer without permanent displacement of medium.
• Transverse and longitudinal wave distinctions.
• Practical observation and measurement reinforce understanding of wave motion.

A wave is a disturbance that transfers energy from one point to another without the transfer of matter. Waves can travel through solids, liquids, or gases, and they exhibit several characteristic features that describe their shape, motion, and speed. Understanding these features is essential for analysing wave behaviour in various physical contexts.

A wavefront is an imaginary line or surface joining points on a wave that have the same phase of vibration. For example, in water waves, wavefronts appear as the crests of the waves moving outward. Wavefronts help visualise the propagation of waves, especially in two or three dimensions.

The shape of a wave can be described by its crests and troughs:

The crest is the highest point on a wave, representing the maximum positive displacement from the rest position. It is where the medium is displaced furthest in one direction. The trough is the lowest point on a wave, representing the maximum negative displacement from the rest position. It is where the medium is displaced furthest in the opposite direction to the crest.

• Wavefront: line or surface of constant phase in a wave.
• Crest: highest point of a wave.
• Trough: lowest point of a wave.

The wavelength (λ) is the distance between two successive points on a wave that are in phase, such as from crest to crest or trough to trough. It is measured in metres (m).

Frequency (f) is the number of complete waves passing a fixed point per second. It is measured in hertz (Hz), where 1 Hz = 1 wave per second.

Frequency is determined by the source of the wave and remains constant as the wave travels through a medium. Wavelength and frequency are inversely related when wave speed is constant.

• Wavelength (λ): distance between two consecutive crests or troughs, measured in metres (m).
• Frequency (f): number of waves passing a point per second, measured in hertz (Hz).

Amplitude (A) is the maximum displacement of a point on the wave from its rest (equilibrium) position. It measures the wave's energy: larger amplitude means more energy is carried by the wave.

Amplitude is measured in metres (m) and is always a positive value. It corresponds to the height of the crest or the depth of the trough relative to the rest position.

• Amplitude (A): maximum displacement from rest position, measured in metres (m).
• Amplitude relates to the energy carried by the wave.

Wave speed (v) is the speed at which the wave propagates through a medium. It depends on the properties of the medium (e.g., tension, density) and the type of wave.

Wave speed is related to frequency and wavelength by the formula:

\[ v = f \times \lambda \] where: \(v\) is wave speed in metres per second (m/s), \(f\) is frequency in hertz (Hz), \(\lambda\) is wavelength in metres (m). This formula can be rearranged to find frequency or wavelength if the other two quantities are known: \( f = \frac{v}{\lambda} \) \( \lambda = \frac{v}{f} \) **Example calculation:** A wave has a frequency of 5 Hz and a wavelength of 2 m. Calculate the wave speed. \[ v = f \times \lambda = 5\,\text{Hz} \times 2\,\text{m} = 10\,\text{m/s} \] **Common error:** Confusing units or forgetting to multiply frequency by wavelength. Always check units and ensure frequency is in Hz and wavelength in metres before calculating wave speed.

• Wave speed (v) = frequency (f) × wavelength (λ).
• Units: v in m/s, f in Hz, λ in m.
• Rearrangements: f = v/λ, λ = v/f.
• Example: For f = 5 Hz and λ = 2 m, v = 10 m/s.

A wave is a disturbance that transfers energy from one point to another without transferring matter. Three key properties describe waves: frequency, wavelength, and wave speed.

Frequency (f) is the number of complete waves passing a point each second. It is measured in hertz (Hz), where 1 Hz = 1 wave per second.

Wavelength (λ) is the distance between two successive points in phase on a wave, such as crest to crest or trough to trough. It is measured in metres (m). Wave speed (v) is the distance a wave travels per unit time, measured in metres per second (m/s).

• Frequency (f): number of waves per second, unit Hz
• Wavelength (λ): distance between successive crests or troughs, unit m
• Wave speed (v): distance travelled by wave per second, unit m/s

The speed of a wave is related to its frequency and wavelength by the formula:

v = f × λ, where: v is wave speed (m/s), f is frequency (Hz), and λ is wavelength (m).

This formula shows that wave speed is the product of how many waves pass a point each second and the length of each wave.

• Wave speed (v) = frequency (f) × wavelength (λ)
• Units must be consistent: v in m/s, f in Hz, λ in m

The formula can be rearranged to find frequency or wavelength if wave speed and one other quantity are known:

To find frequency: f = v / λ (frequency equals wave speed divided by wavelength)

To find wavelength: λ = v / f (wavelength equals wave speed divided by frequency)

• f = v / λ (frequency)
• λ = v / f (wavelength)

A water wave has a frequency of 2 Hz and a wavelength of 0.5 m. Calculate its speed.

Step 1: Write down the formula: v = f × λ Step 2: Substitute values: v = 2 Hz × 0.5 m Step 3: Calculate: v = 1 m/s Step 4: State the answer with units: The wave speed is 1 metre per second (1 m/s).

• Formula: v = f × λ
• Substitution: v = 2 × 0.5
• Calculation: v = 1 m/s
• Answer: Wave speed = 1 m/s

A frequent mistake is mixing units or forgetting to convert units before calculation. Always ensure frequency is in hertz and wavelength in metres.

Another common error is confusing frequency and wavelength or using the wrong formula rearrangement.

Remember that frequency and wavelength are inversely proportional for a constant wave speed: if frequency increases, wavelength decreases, and vice versa.

• Always use consistent units: Hz for frequency, m for wavelength, m/s for speed
• Check which quantity to find and rearrange formula accordingly
• Frequency and wavelength are inversely related for a fixed wave speed

A transverse wave is a wave in which the particles of the medium vibrate at right angles (perpendicular) to the direction in which the wave travels. This means if the wave moves horizontally, the vibrations occur vertically or in a direction perpendicular to the wave's travel direction.

The key characteristic of transverse waves is this perpendicular vibration, which contrasts with longitudinal waves where vibrations are parallel to wave travel.

In transverse waves, energy is transferred through the medium by these perpendicular oscillations, but the particles themselves do not travel with the wave; they oscillate about fixed positions.

• Vibration direction ⟂ (perpendicular) to wave travel direction.
• Energy transfer occurs without net movement of particles.
• Particles oscillate about fixed equilibrium positions.

Several important physical phenomena can be modelled as transverse waves:

1. Electromagnetic Radiation: This includes visible light, radio waves, X-rays, and other electromagnetic waves. These waves consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of wave propagation. Electromagnetic waves do not require a medium and can travel through a vacuum.

2. Water Waves: On the surface of water, waves cause water particles to move in circular or elliptical paths, but the dominant motion of the wave crest and trough is perpendicular to the direction of wave travel, making surface water waves transverse in nature at the surface level, although water waves have some longitudinal components below the surface as well. The visible up-and-down motion of the water surface is a transverse vibration relative to the horizontal wave travel direction on the surface of the water body (e.g., a ripple tank). 3. Seismic S-Waves (Secondary Waves): These are a type of seismic wave generated by earthquakes. S-waves move through the Earth by causing particles to vibrate perpendicular to the wave direction. They cannot travel through liquids, which helps seismologists understand Earth's internal structure.

• Electromagnetic waves: oscillating electric and magnetic fields perpendicular to wave travel.
• Water waves: surface particles move up and down while wave travels horizontally.
• Seismic S-waves: particles vibrate perpendicular to wave direction; cannot travel through liquids.

In a transverse wave, the energy transfer occurs through the oscillation of particles perpendicular to the wave's travel direction. For example, if a rope is shaken up and down at one end, waves travel along the rope horizontally, but the rope's particles move vertically.

This perpendicular vibration causes crests (points of maximum positive displacement) and troughs (points of maximum negative displacement) to form and move along the wave path.

The wave speed (v) depends on the medium's properties, such as tension and mass per unit length in a string, or elasticity and density in solids for seismic waves.

• Particles oscillate perpendicular to wave travel direction, creating crests and troughs.
• Energy propagates along the wave direction, not by particle transport.
• Wave speed depends on medium properties (e.g., tension, density).

It is important to distinguish transverse waves from longitudinal waves:

In transverse waves, vibrations are perpendicular to wave travel direction.

In longitudinal waves, vibrations are parallel to wave travel direction, such as sound waves and seismic P-waves (primary waves). Understanding this difference helps identify wave types in various physical contexts and their propagation characteristics.

• Transverse: vibration ⟂ wave direction.
• Longitudinal: vibration ∥ wave direction.
• Examples: transverse – light, water waves, S-waves; longitudinal – sound, P-waves.

To draw a transverse wave diagram: 1. Draw a horizontal straight line to represent the equilibrium position of the medium.

2. Draw a sinusoidal curve above and below this line to represent the wave.

3. Label the horizontal axis as 'Direction of wave travel' (e.g., in metres, m). 4. Label the vertical axis as 'Displacement of particles' (e.g., in metres, m). 5. Indicate the crest (highest point) and trough (lowest point) on the wave. 6. Draw an arrow perpendicular to the wave travel direction to show the vibration direction of particles (up and down). This diagram visually emphasises that the particle displacement is perpendicular to the wave propagation direction.

• Horizontal axis: wave travel direction (distance).
• Vertical axis: particle displacement (amplitude).
• Crests and troughs show maximum positive and negative displacement.
• Vibration direction arrow perpendicular to wave travel direction.

A longitudinal wave is a wave in which the particles of the medium vibrate parallel to the direction in which the wave travels. This means that as the wave moves forward, particles oscillate back and forth along the same line as the wave's propagation.

The oscillation involves regions where particles are compressed together (compressions) and regions where particles are spread apart (rarefactions). These alternating compressions and rarefactions travel through the medium, transferring energy from one place to another without the net movement of matter.

In contrast to transverse waves, where particle vibration is perpendicular to wave travel, longitudinal waves have particle motion aligned with wave direction.

• Particle vibration direction is parallel to wave travel direction.
• Energy transfer occurs via compressions and rarefactions.
• No net transport of matter occurs; only energy moves.

In a longitudinal wave, compressions are regions where particles are closer together than normal, resulting in higher pressure and density. Rarefactions are regions where particles are further apart, resulting in lower pressure and density.

As the wave propagates, these compressions and rarefactions move through the medium, causing particles to oscillate about their equilibrium positions.

The speed of the wave depends on the properties of the medium, such as its elasticity and density. For example, sound waves travel faster in solids than in gases because particles are closer and more tightly bound, facilitating quicker transmission of compressions and rarefactions.

• Compressions: high pressure, particles close together.
• Rarefactions: low pressure, particles spread apart.
• Wave speed depends on medium's elasticity and density.

Sound waves in air are classic examples of longitudinal waves. When an object vibrates, it causes air particles nearby to oscillate parallel to the direction of wave travel, creating compressions and rarefactions that propagate through the air.

The frequency of the sound wave corresponds to the rate of vibration of the source and determines the pitch of the sound. The amplitude relates to the loudness.

Sound waves require a medium (solid, liquid, or gas) to travel because they rely on particle interactions to transmit energy. They cannot travel through a vacuum.

• Sound waves involve air particle vibrations parallel to wave travel.
• Frequency determines pitch; amplitude determines loudness.
• Require a medium; cannot travel in vacuum.

Seismic P-waves (primary waves) generated by earthquakes are longitudinal waves that travel through the Earth’s interior.

These waves cause particles in rocks to vibrate back and forth in the same direction as the wave travels, producing compressions and rarefactions in the Earth's materials.

P-waves are the fastest seismic waves and can travel through solids, liquids, and gases, making them important for studying Earth's internal structure.

• P-waves cause particle vibration parallel to wave travel.
• They produce compressions and rarefactions in Earth materials.
• Travel through solids, liquids, and gases; fastest seismic waves.

A standard diagram of a longitudinal wave shows a horizontal line representing the medium at rest.

Along this line, regions of compressions are drawn as closely spaced vertical lines or shaded areas, and rarefactions as widely spaced lines or gaps.

To draw: start with a horizontal baseline, mark compressions as dense clusters of vertical lines, and rarefactions as spaced-out lines, indicating particle density variations along the wave direction.

• Draw horizontal baseline for medium at rest.
• Mark compressions as dense vertical lines or shaded regions.
• Mark rarefactions as spaced vertical lines or gaps.
• Label wave direction and particle vibration direction as parallel.

Reflection occurs when a wave encounters a boundary or surface that it cannot pass through and bounces back into the original medium.

The law of reflection states that the angle of incidence (the angle between the incoming wave and the normal to the surface) is equal to the angle of reflection (the angle between the reflected wave and the normal).

This applies to all types of waves, including light, sound, and water waves, when they meet a flat, smooth surface such as a mirror or a calm water surface.

• Angle of incidence = Angle of reflection
• The incident wave, reflected wave, and the normal all lie in the same plane
• Reflection preserves the wave’s frequency and speed in the original medium

Refraction is the change in direction of a wave as it passes from one medium into another where its speed is different.

This change in speed causes the wave to bend at the boundary between the two media.

For example, light waves slow down when entering glass from air, causing them to bend towards the normal; conversely, they speed up when moving from glass to air, bending away from the normal.

• Refraction occurs due to a change in wave speed between media
• The amount of bending depends on the relative speeds and refractive indices of the two media
• Refractive index, n = speed of wave in vacuum (or air) ÷ speed in medium
• Snell’s Law relates angles and refractive indices: n₁ sin θ₁ = n₂ sin θ₂
• Wave frequency remains constant; wavelength changes in the new medium

Diffraction is the spreading out of waves when they pass through a narrow gap or around an obstacle.

The extent of diffraction depends on the size of the gap relative to the wavelength of the wave.

If the gap is similar in size to the wavelength, the waves spread out widely; if the gap is much larger, diffraction is minimal.

• Diffraction causes waves to bend and spread beyond geometric shadow regions
• More pronounced when wavelength ≈ gap size
• Occurs with all wave types: sound, water, light (though light diffraction is less noticeable due to its very short wavelength)

Ray diagrams are used to represent wave fronts and directions of wave travel.

For reflection, draw the incident ray approaching a flat surface, the normal at the point of incidence, and the reflected ray leaving at the same angle as the incident ray.

For refraction, draw the incident ray entering the boundary between two media, the normal, and the refracted ray bending towards or away from the normal depending on speed change (towards normal if slowing down, away if speeding up). Label angles of incidence and refraction accordingly, and indicate the two media with different refractive indices if possible.

• Incident ray, reflected/refracted ray, and normal must be clearly shown
• Angles measured from the normal (perpendicular to the surface)
• For diffraction, represent wave fronts bending around edges or spreading through gaps

Reflection, refraction, and diffraction are fundamental wave behaviours that explain how waves interact with boundaries and openings.

Reflection requires a boundary that does not absorb or transmit the wave.

Refraction requires a change in medium with different wave speeds, causing bending of the wave path according to Snell’s Law and refractive indices of the media involved.

• Diffraction is most noticeable when the wavelength is comparable to the size of the gap or obstacle
• Wave frequency remains constant during reflection and refraction; only speed and wavelength change during refraction
• Understanding these behaviours is essential for applications such as optics, acoustics, and wave technology

A ripple tank is a shallow glass tank filled with water, used to generate and observe water waves on the surface. A motor-driven dipper or vibrator creates regular waves, which travel across the tank. A light source above the tank projects the wave patterns onto a screen below, allowing clear visualisation of wavefronts and their interactions with obstacles or boundaries.

The ripple tank is ideal for demonstrating fundamental wave behaviours such as reflection, refraction, and diffraction because water waves are slow and visible, making wave properties easier to study than in other wave types.

• Apparatus includes ripple tank, motor-driven dipper, light source, screen, flat barriers, blocks of varying depth, and obstacles with gaps.

Reflection occurs when waves encounter a boundary that they cannot pass through, such as a flat vertical barrier placed in the ripple tank. The waves bounce back into the original medium.

The law of reflection states: the angle of incidence equals the angle of reflection. Both angles are measured between the wavefront and the normal (a line perpendicular) to the reflecting surface.

In the ripple tank, wavefronts approach the flat barrier at an angle. Upon reaching the barrier, the waves reflect such that the angle between the incident wavefront and the normal equals the angle between the reflected wavefront and the normal. This can be observed by tracing the wavefronts on the screen or drawing wavefront diagrams.

• Set up a flat vertical barrier in the ripple tank.
• Generate plane waves at an angle to the barrier.

Refraction is the change in direction of waves when they pass from one medium to another in which their speed differs. In a ripple tank, this is demonstrated by having regions of different water depths.

Water waves travel faster in deeper water and slower in shallower water. When waves cross the boundary between deep and shallow regions at an angle, their speed changes, causing the wavefronts to bend.

The relationship between wave speed (v), frequency (f), and wavelength (λ) is v = fλ. Since frequency remains constant, a change in speed results in a change in wavelength, which causes the wave to change direction according to Snell's law for waves: sin i / sin r = v₁ / v₂, where i is the angle of incidence, r the angle of refraction, and v₁ and v₂ the wave speeds in the respective depths.

• Place a block in the ripple tank to create a shallow region.
• Generate plane waves approaching the boundary at an angle.
• Observe the bending of wavefronts at the boundary.

Diffraction is the spreading out of waves when they pass through a narrow gap or around an obstacle's edge.

In the ripple tank, placing a barrier with a gap or an obstacle with a sharp edge causes waves to spread out beyond the gap or around the edge.

The amount of diffraction depends on the size of the gap relative to the wavelength. If the gap is similar in size or smaller than the wavelength, diffraction is more pronounced; if the gap is much larger, waves pass through with little spreading.

• Set up a barrier with a narrow gap or an obstacle with a sharp edge.
• Generate plane waves approaching the gap or edge.

To perform ripple tank experiments effectively: ensure the water surface is calm and the dipper produces regular waves.

Use a stroboscopic light or a lamp and screen to clearly see wavefronts.

Measure angles using a protractor placed beneath the screen or by drawing wavefront diagrams on tracing paper over the projected image. Wavefronts are lines joining points of the same phase (e.g., crests). The direction of wave travel is perpendicular to wavefronts, indicated by rays drawn at right angles to wavefronts towards the direction of propagation.

• Control variables such as wave frequency, water depth, and gap size.

Diffraction is the phenomenon where waves bend around the edges of an obstacle or spread out after passing through a narrow gap. It occurs with all types of waves, including water waves, sound waves, and light waves.

Diffraction is most noticeable when the size of the obstacle or gap is comparable to the wavelength of the wave. The bending causes the wavefronts to spread out beyond the geometrical shadow of the obstacle or gap.

This spreading effect is a fundamental property of wave behaviour and demonstrates that waves do not always travel in straight lines.

• Diffraction = bending and spreading of waves around edges or through gaps.
• Occurs for all wave types: sound, light, water, etc.
• Most significant when gap size ≈ wavelength.

The wavelength (λ) of a wave is the distance between two consecutive points in phase, such as crest to crest or trough to trough, measured in metres (m).

Longer wavelengths diffract more because the wavefronts can bend more easily around obstacles or through gaps of similar size.

Shorter wavelengths diffract less and tend to travel in straighter paths when passing through the same gap size.

• Wavelength (λ) measured in metres (m).
• Longer λ → greater diffraction.
• Shorter λ → less diffraction.

The size of the gap (often called the aperture width) is the physical width of the opening through which the wave passes, measured in metres (m).

When the gap size is large compared to the wavelength, the wave passes through with little bending and continues mostly straight.

When the gap size is small or comparable to the wavelength, the wave spreads out widely after passing through the gap.

• Gap size measured in metres (m).
• Large gap (≫ λ) → minimal diffraction.
• Small gap (≈ λ) → significant diffraction.

The extent of diffraction depends on the ratio of the wavelength to the gap size. This can be summarised as:

If λ ≈ gap size, diffraction is strong and waves spread widely.

If λ ≪ gap size, diffraction is weak and waves travel mostly straight through the gap.

• Diffraction depends on λ / gap size ratio.
• λ ≈ gap size → strong diffraction, wide spreading.
• λ ≪ gap size → weak diffraction, narrow spreading.

In practical situations, such as sound passing through a doorway or light through a slit, the amount of diffraction affects how waves propagate beyond the opening.

To draw a diffraction diagram: 1) Draw a straight barrier with a gap of known width.

2) Draw incident wavefronts approaching the gap, spaced by the wavelength λ, perpendicular to the barrier line. 3) After the gap, draw wavefronts spreading out in semicircular arcs if λ ≈ gap size, showing strong diffraction. 4) If λ ≪ gap size, draw wavefronts continuing straight with little spreading.

• Diffraction affects wave propagation in real life (e.g., sound through doors).
• Diagram: barrier with gap, incident wavefronts, spreading wavefronts after gap.
• Strong diffraction: semicircular spreading wavefronts.
• Weak diffraction: straight wavefronts continuing.

Diffraction is the phenomenon where waves bend around the edges of obstacles or spread out after passing through narrow openings. This bending occurs because waves propagate in all directions from a point on the wavefront when obstructed or constrained.

Diffraction is a fundamental property of all types of waves, including sound waves, water waves, and electromagnetic waves such as light. It is most noticeable when the size of the obstacle or gap is comparable to the wavelength of the wave.

• Diffraction is the bending of waves around edges or through gaps.
• It occurs for all wave types: sound, light, water, etc.
• Diffraction effects are more pronounced when obstacle size ≈ wavelength.

The extent of diffraction depends primarily on the wavelength of the wave relative to the size of the obstacle or gap it encounters. Longer wavelengths diffract more significantly, bending around edges and spreading out more than shorter wavelengths.

When the wavelength is much smaller than the size of the obstacle or gap, diffraction is minimal and the wave travels mostly straight. Conversely, when the wavelength is similar to or larger than the obstacle size, the wave bends considerably, spreading into the region behind the obstacle.

This relationship can be summarised as: the greater the wavelength compared to the obstacle size, the greater the diffraction.

• Diffraction increases as wavelength increases relative to obstacle size.
• Waves with long wavelengths bend more around edges.
• Waves with short wavelengths show little diffraction and travel straight.

Sound waves typically have wavelengths ranging from millimetres to metres, depending on frequency. Because these wavelengths are often comparable to everyday obstacles such as doorways or corners, sound waves diffract significantly, allowing us to hear sounds even when the source is not in direct line of sight.

Light waves have much shorter wavelengths, on the order of hundreds of nanometres (10⁻⁷ m). Since everyday objects are much larger than these wavelengths, light waves diffract very little around edges, which is why shadows have sharp edges and light does not bend noticeably around corners.

This difference explains why sound can be heard around obstacles but light cannot be seen around them.

• Sound wavelengths are long, causing strong diffraction around obstacles.
• Light wavelengths are very short, causing minimal diffraction.
• This explains why sound bends around corners but light casts sharp shadows.

Diffraction affects many practical situations. For example, radio waves, which have long wavelengths, can bend around hills and buildings, enabling communication beyond line of sight. In contrast, visible light cannot do this, limiting optical communication to direct paths.

In optical instruments, diffraction limits the resolution because light waves spread out after passing through small apertures, affecting image sharpness.

Understanding diffraction is essential in designing devices such as speakers, antennas, and optical instruments to optimise wave propagation and reception.

• Radio waves diffract around large obstacles, aiding communication.
• Diffraction limits resolution in optical devices.
• Design of wave-based devices considers diffraction effects.

To draw a diagram illustrating diffraction at an edge:

1. Draw a straight barrier with a single sharp edge on the right side of the page.

2. Represent incoming wavefronts as several parallel straight lines approaching the edge from the left, spaced evenly to indicate wavelength λ (label this). Each line is perpendicular to the wave direction (left to right). 3. Beyond the edge, draw the wavefronts bending around the edge, forming curved lines spreading into the shadow region behind the barrier, showing diffraction. 4. Indicate that the amount of bending depends on wavelength: longer wavelengths bend more widely, shorter wavelengths bend less.

• Draw parallel wavefronts approaching an edge.
• Show wavefronts bending around the edge after the barrier.
• Label wavelength λ and indicate bending extent depends on λ.