🔍 Detailed Explanation of the Properties of Waves (Transverse and Longitudinal)
🌊 What Are Waves?
A wave is a disturbance that travels through a medium (like air, water, or solid materials) or even through empty space, carrying energy without transporting matter permanently.
↕️ Transverse Waves
Definition:
In transverse waves, the particles of the medium vibrate perpendicular (at right angles) to the direction in which the wave travels.
Characteristics:
- The movement of particles is up and down while the wave moves horizontally (left to right or right to left).
- Transverse waves have crests (the highest points) and troughs (the lowest points).
- The distance between two crests or two troughs is called the wavelength.
- The amplitude is the maximum height of the wave from its rest position, showing how much energy the wave has.
- Examples include waves on water, electromagnetic waves (like light and radio waves), and waves on a string.
Example:
When you flick a rope up and down, the wave created moves along the rope, but the rope itself moves up and down, showing transverse wave motion.
↔️ Longitudinal Waves
Definition:
In longitudinal waves, the particles of the medium vibrate parallel to the direction of wave travel.
Characteristics:
- The particles move back and forth in the same direction as the wave.
- Longitudinal waves consist of compressions (where particles are close together) and rarefactions (where particles are spread apart).
- The wavelength is the distance between two compressions or two rarefactions.
- The amplitude relates to the amount of compression of the particles.
- Sound waves in air are a common example of longitudinal waves.
Example:
When a slinky is pushed and pulled along its length, the coils move forward and backward along the slinky, which shows the motion of longitudinal waves.
⚖️ Comparing Transverse and Longitudinal Waves
| Property | Transverse Waves | Longitudinal Waves |
|---|---|---|
| Particle vibration | Perpendicular to wave direction | Parallel to wave direction |
| Wave features | Crests and troughs | Compressions and rarefactions |
| Examples | Water waves, light waves | Sound waves, seismic P-waves |
📝 Key Terms to Remember
- Wavelength: Distance between two points in phase (like crest to crest or compression to compression).
- Amplitude: Maximum displacement from the rest position, related to wave energy.
- Frequency: Number of waves passing a point per second, measured in hertz (Hz).
- Speed: How fast the wave travels through the medium.
📚 Summary
Understanding the properties of waves helps explain many natural phenomena. Transverse waves move energy with particle motion at right angles to the wave direction, seen in water and light waves. Longitudinal waves move energy with particles moving parallel to the wave direction, like sound waves travelling through air.
Try to visualise these with simple experiments, like moving a rope for transverse waves or using a slinky for longitudinal waves, to get a clear picture of how wave energy transfers through different media.
📝 10 Examination-Style 1-Mark Questions on Properties of Waves
- What type of wave is light: transverse or longitudinal?
Answer: Transverse - In which type of wave do particles move parallel to the direction of the wave?
Answer: Longitudinal - What is the highest point of a transverse wave called?
Answer: Crest - What is the term for the distance between two consecutive crests or troughs in a wave?
Answer: Wavelength - In a longitudinal wave, what are the regions where particles are closest together called?
Answer: Compressions - What property of a wave is measured in hertz (Hz)?
Answer: Frequency - What do we call the lowest point of a transverse wave?
Answer: Trough - What term describes the distance from the rest position to the crest in a wave?
Answer: Amplitude - What is the name of the areas where particles are spread apart in a longitudinal wave?
Answer: Rarefactions - What property of a wave determines how fast it travels through a medium?
Answer: Speed
🧠 10 Examination-Style 2-Mark Questions on Properties of Waves
- What type of wave is a light wave and why?
A light wave is a transverse wave because its vibrations are perpendicular to the direction of wave travel. - Describe the particle motion in a longitudinal wave.
In a longitudinal wave, particles vibrate parallel to the direction of wave energy transfer. - Name one example of a transverse wave and one example of a longitudinal wave.
An example of a transverse wave is a wave on a string, and an example of a longitudinal wave is a sound wave in air. - How does the wavelength of a wave relate to the distance between compressions in a longitudinal wave?
The wavelength is the distance between two consecutive compressions or rarefactions in a longitudinal wave. - What property of a wave changes when the wave speed increases but frequency stays the same?
The wavelength increases when the wave speed increases and frequency remains constant. - Explain how the amplitude of a wave relates to its energy.
The amplitude of a wave is directly related to its energy; greater amplitude means more energy. - What is the difference between transverse and longitudinal waves in terms of particle displacement?
In transverse waves, particles move perpendicular to the wave direction, whereas in longitudinal waves, particles move parallel. - How can you identify a transverse wave from its graphical representation?
A transverse wave can be identified by oscillations moving up and down or side to side, perpendicular to the wave direction. - What causes compressions and rarefactions in a longitudinal wave?
Compressions and rarefactions are caused by particles being pushed together and pulled apart as the wave moves through the medium. - Why can sound not travel through a vacuum?
Sound cannot travel through a vacuum because it requires a medium’s particles to vibrate for energy transfer.
✍️ 10 Examination-Style 4-Mark Questions on Properties of Waves (Transverse and Longitudinal)
Question 1:
Define transverse waves and describe two key characteristics that distinguish them from longitudinal waves.
Answer:
Transverse waves are waves where the oscillations or vibrations are perpendicular to the direction of energy transfer. This means that the particles move up and down or side to side while the wave moves forward. One key characteristic is the presence of peaks (crests) and troughs, which are the highest and lowest points of the wave respectively. Another characteristic is that transverse waves can travel through solids and on surfaces like water but not through gases or liquids as easily. Examples include light waves and water waves. This is different from longitudinal waves, where particles vibrate parallel to the wave’s direction.
Question 2:
Explain what longitudinal waves are and give an everyday example.
Answer:
Longitudinal waves are waves in which the particles of the medium vibrate parallel to the direction that the wave travels. This creates areas of compression, where particles are close together, and rarefaction, where particles are spread apart. A common example of a longitudinal wave is a sound wave traveling through air. When someone speaks, sound waves cause the air particles to vibrate back and forth in the same direction as the wave moves towards our ears. These vibrations allow energy to transfer from the source of the sound to our eardrums.
Question 3:
Describe how the amplitude of a wave relates to the energy it carries.
Answer:
The amplitude of a wave is the maximum displacement of particles from their rest position. It is directly related to the energy carried by the wave: the bigger the amplitude, the more energy the wave has. For example, a wave with a large amplitude will cause particles to move further away from their normal position, which means it transfers more energy to the surroundings. This is true for both transverse and longitudinal waves. In sound waves, a larger amplitude means a louder sound. In water waves, a larger amplitude means bigger waves.
Question 4:
What is the difference between a wave’s wavelength and its frequency?
Answer:
Wavelength is the distance between two corresponding points on consecutive waves, such as from crest to crest in transverse waves or from compression to compression in longitudinal waves. It tells you how long one wave is. Frequency, on the other hand, is how many waves pass a point in one second, measured in hertz (Hz). Frequency determines the pitch in sound waves or the colour in light waves. Wavelength and frequency have an inverse relationship: if the wavelength increases, the frequency decreases, meaning fewer waves pass per second, and vice versa.
Question 5:
Explain what happens to the speed of a wave when it moves from one medium to another.
Answer:
When a wave moves from one medium to another, its speed changes depending on the properties of the new medium, such as density and elasticity. For example, sound waves travel faster in solids than in air because the particles are closer together in solids, making it easier for the vibrations to pass through. Similarly, light waves slow down when they enter denser materials, like glass or water, compared to air. The change in speed often causes the wave to change direction, a process called refraction. The frequency remains the same during this change, but the wavelength adjusts according to the new speed.
Question 6:
Describe what is meant by the terms ‘compression’ and ‘rarefaction’ in longitudinal waves.
Answer:
In longitudinal waves, ‘compression’ refers to regions where the particles of the medium are pushed close together, resulting in high pressure and density. ‘Rarefaction’ is the opposite; it is the region where particles are spread apart, creating low pressure and density. These compressions and rarefactions travel along the direction of the wave and are essential parts of how the wave transfers energy. For example, sound waves in air consist of successive compressions and rarefactions moving through the air as the wave carries sound energy to our ears.
Question 7:
How can you distinguish between a transverse wave and a longitudinal wave using a diagram?
Answer:
In a diagram, a transverse wave is shown as a wave with peaks (crests) and troughs where the wave oscillates perpendicular to the wave’s direction. The particles move up and down, while the energy moves horizontally. In contrast, a longitudinal wave diagram has compressions and rarefactions, where particles are shown moving back and forth in the same direction as the wave travels. The particles’ vibrations are parallel to the energy transfer direction. Using these visual differences, you can easily identify which wave is transverse and which is longitudinal.
Question 8:
Why can sound not travel through a vacuum, but light can?
Answer:
Sound cannot travel through a vacuum because it is a longitudinal wave that requires particles to vibrate and transfer energy. In a vacuum, there are no particles or medium for the sound waves to move through, so the vibrations cannot be passed on. Light, however, is an electromagnetic wave and does not need a medium to travel; it can move through vacuums because it is a combination of electric and magnetic fields oscillating perpendicular to each other. This is why we can see sunlight in space but cannot hear any sound in space.
Question 9:
What is the relationship between wave speed, frequency, and wavelength? How can one calculate wave speed?
Answer:
The relationship between wave speed (v), frequency (f), and wavelength (λ) is given by the formula: v = f × λ. This means the speed of a wave is equal to its frequency multiplied by its wavelength. The frequency is how many waves pass a point every second, and the wavelength is the distance between two corresponding points of the wave. Using this equation, if you know the frequency and wavelength, you can calculate the wave speed by multiplying them. This formula applies to all types of waves, including transverse and longitudinal.
Question 10:
Describe the energy transfer in waves and explain whether the particles of the medium are transported with the wave.
Answer:
Waves transfer energy from one place to another without transferring matter. The particles of the medium vibrate around their fixed positions but do not travel with the wave. In transverse waves, particles move perpendicular to the wave direction, while in longitudinal waves, particles vibrate parallel to it. Energy is passed from one particle to the next through these oscillations, but the particles themselves remain in roughly the same place. This is why a wave can move across long distances but the medium itself does not move along with the wave.
🔬 10 Examination-Style 6-Mark Questions on Properties of Waves: Transverse and Longitudinal Waves
Question 1
Describe the main differences between transverse and longitudinal waves, including how particles move in each type of wave.
Answer:
Transverse waves have particles that move perpendicular to the direction of the wave’s energy transfer. For example, in water waves, the water moves up and down while the wave travels forward. In longitudinal waves, particles vibrate parallel to the direction of energy transfer, like sound waves in air where air particles compress and rarefy along the path of the wave. Transverse waves have peaks (crests) and valleys (troughs), while longitudinal waves have compressions (regions of high pressure) and rarefactions (regions of low pressure). Both types carry energy without transferring particles themselves; the particles only oscillate around their fixed positions. Transverse waves can travel through solids and on surfaces, but longitudinal waves can also travel through gases and liquids. Understanding these differences helps explain why sound cannot travel through a vacuum, but electromagnetic waves (which are transverse) can.
Question 2
Explain how energy is transferred through a longitudinal wave, using sound as an example, and describe the roles of compressions and rarefactions.
Answer:
In a longitudinal wave like sound, energy is transferred through successive compressions and rarefactions. Compressions are areas where particles are pushed close together, creating regions of high pressure. Rarefactions are areas where particles are spread apart, creating low-pressure regions. The sound wave travels as particles vibrate back and forth parallel to the wave’s direction, pushing the adjacent particles in a chain-like manner. This series of compressions and rarefactions moves through the medium, carrying energy from the source to the receiver. The particles themselves do not move along with the wave but only oscillate about their fixed positions. The energy carried by the wave allows us to hear sounds when the vibrating air particles cause our eardrums to vibrate.
Question 3
Describe how the wavelength, frequency, and speed of a transverse wave are related and how changing one affects the others.
Answer:
The relationship between wavelength, frequency, and speed for any wave, including transverse waves, is given by the equation: speed = frequency × wavelength. The wavelength is the distance between two consecutive crests or troughs in the wave. Frequency is how many waves pass a point every second, measured in hertz (Hz). Wave speed depends on the medium the wave is travelling through. If the frequency increases while the speed remains constant, the wavelength must decrease, because more waves are produced in the same amount of time, meaning the distance between each crest is smaller. Conversely, if wavelength increases while speed remains the same, frequency decreases. This relationship is important for understanding wave properties in different materials and situations.
Question 4
Explain what happens to the particles in a transverse wave as it moves through a solid medium like a spring or a rope.
Answer:
In a transverse wave travelling through a solid like a spring or rope, the particles vibrate perpendicular to the direction of the wave’s travel. If the wave is moving horizontally along the rope, particles move up and down. As the wave passes, particles are displaced from their resting positions and then return. This creates crests where particles reach the highest points and troughs where they are at the lowest. The energy moves forward along the rope, but the particles only move in a small oscillating motion vertically. This motion helps transfer the wave’s energy without the actual particles moving along the rope. The rigidity of solids allows this perpendicular vibration to happen easily, compared to gases or liquids where particles are more loosely packed.
Question 5
Using a diagram, describe how compressions and rarefactions form in a longitudinal wave.
Answer:
In a longitudinal wave, compressions and rarefactions are created by the forward and backward movement of particles in the medium. When particles push closer together, they form a compression, which appears as a dense region in the diagram. When particles spread apart, they form a rarefaction, which is a less dense or stretched-out region. A diagram would show a series of compressions and rarefactions along the wave’s direction of travel. The wave moves horizontally, and these alternating regions indicate areas of higher and lower pressure. The wave’s energy is carried through this process as the particles keep oscillating back and forth but do not travel with the wave itself.
Question 6
Explain why transverse waves cannot travel through gases and liquids but longitudinal waves can.
Answer:
Transverse waves require particles in the medium to be able to move perpendicular to the wave’s direction and resist shear forces. Solids have particles tightly packed and bonded strongly enough to support this sideways motion. In gases and liquids, particles are free to move past each other and cannot resist these forces, so transverse waves cannot form or travel well. Longitudinal waves, however, only require particles to move back and forth along the wave direction, creating alternating compressions and rarefactions. Because gases and liquids can be compressed and expanded, longitudinal waves like sound waves easily travel through them. This explains why sound (longitudinal) travels through air but light or waves on a string (transverse) cannot.
Question 7
Discuss how the amplitude of a transverse wave affects the energy it carries.
Answer:
The amplitude of a transverse wave is the maximum displacement of particles from their resting position, measured from the middle line to a crest or trough. A larger amplitude means particles move more, indicating more energy in the wave. This is why waves with higher amplitude are perceived as louder sounds or brighter light, depending on the wave type. Energy in waves is proportional to the square of the amplitude, so doubling the amplitude increases the wave’s energy by four times. Thus, higher amplitude waves transfer more energy through the medium, affecting how intense the wave effect is perceived.
Question 8
Describe what is meant by the terms ‘crest’, ‘trough’, ‘compression’, and ‘rarefaction’ in the context of waves.
Answer:
In waves, a ‘crest’ is the highest point reached by particles in a transverse wave during the oscillation. In contrast, a ‘trough’ is the lowest point. These terms apply to transverse waves where particles move perpendicular to wave direction. For longitudinal waves, ‘compression’ refers to regions where particles are closest together, meaning the pressure is higher than normal. ‘Rarefaction’ indicates areas where particles are spread apart, creating regions of lower pressure. These terms help us describe the pattern and behaviour of waves, showing how energy causes particles to oscillate and produce different wave parts.
Question 9
Explain why sound waves are classified as longitudinal waves, using particle movement as part of your explanation.
Answer:
Sound waves are longitudinal waves because their particles vibrate parallel to the direction the wave travels. When a sound wave moves through air, air particles oscillate back and forth along the same line as the wave propagation. This causes compressions, where particles crowd together, and rarefactions, where particles are spread out. This pattern of compression and rarefaction moves through the air as the sound energy travels. Since particle motion is along the same direction as the wave, sound waves are longitudinal, unlike transverse waves where particles move perpendicular.
Question 10
Describe what happens to a transverse wave as it passes through a boundary between two different media.
Answer:
When a transverse wave passes from one medium to another (like from air to water), several things can happen at the boundary. Some of the wave’s energy may be reflected back, while the rest is transmitted into the new medium. The wave speed changes because different media have different densities and elastic properties. This change in speed causes the wavelength to change while the frequency stays the same. The wave can also be refracted, meaning its direction changes. The amplitude might reduce due to energy loss in the transfer. Understanding these changes helps explain how waves behave in different environments, such as light waves bending or water waves changing speed.
