Theme C — Wave Behaviour
C.2.2 Transverse and Longitudinal Waves — IB Physics HL Revision Notes & Topical Questions
5 min read 11 parts Lesson 13 of 37 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
C.2.2 Transverse and Longitudinal Waves — IB PHYSICS SL notes: Distinguish transverse from longitudinal waves, interpret their graphs and explain polarization of transverse waves.Classification — compare the direction in which particles or fields oscillate with the direction in w…
- Particles stay put
- Energy transfer
- Compression
- Rarefaction
- Wavelength
- Slinky picture
Part 1 of 9Direction of oscillation versus travel
Direction of oscillation versus travel
Classification
- Classification compare the direction in which particles or fields oscillate with the direction in which energy travels
Particles stay put
- Particles stay put in mechanical waves particles oscillate about fixed points and do not travel along the wave
- All particles have the same motion but are displaced slightly in time, creating the illusion of one moving pattern.
Part 2 of 9Transverse waves
Transverse wave
- Transverse wave a wave in which the oscillations are perpendicular to the direction of motion and energy transfer
- Each particle vibrates up and down.
Pattern
- Pattern crests (peaks) and troughs
Examples
- Examples electromagnetic waves such as radio, visible light and UV,
- and mechanical waves such as vibrations on a guitar string, a rope or approximately water ripples
Vacuum
- Vacuum electromagnetic transverse waves need no particles, so UV from the Sun reaches us across space
Part 3 of 9Longitudinal waves
Longitudinal wave
- Longitudinal wave a wave in which the oscillations are parallel to the direction of motion and energy transfer
- Each particle vibrates back and forth along the line of travel.
Examples
- Examples sound, ultrasound, compression waves in a spring and P-waves in the Earth
Medium
- Medium they are mechanical waves and need particles, so they cannot travel through a vacuum
- Nothing can be heard in outer space.
Energy transfer
- Energy transfer vibrating particles pass energy to neighbours, which produces a compression further along
Part 4 of 9Compressions and rarefactions
Compression
- Compression a region where particles are squeezed closer together, so pressure is above average
Rarefaction
- Rarefaction a region where particles are further apart, so pressure is below average
Wavelength
- Wavelength the distance between two successive compressions or two successive rarefactions
Slinky picture
- Slinky picture each coil moves back and forth along the slinky while the compressions travel along it at the wave speed
- At the centre of a compression the coil has zero displacement.
- Coils on either side are displaced towards the centre.
Part 5 of 9Graphs of longitudinal waves
Plot
- Plot displacement against distance, with positive displacement meaning a shift in the direction of travel
Warning
- Warning the sine-shaped graph is not a picture of the medium; it only plots displacement against position
Compression centre
- Compression centre the curve crosses zero going from positive to negative
Rarefaction centre
- Rarefaction centre the curve crosses zero going from negative to positive
Pressure
- Pressure it is a quarter of a cycle out of phase with displacement
- Pressure is maximum at a compression centre, where the displacement is zero.
Part 6 of 9Polarization
Plane-polarized wave
- Plane-polarized wave a transverse wave whose oscillations lie in a single plane
Unpolarized light
- Unpolarized light light from the Sun or a lamp is a mixture of all planes perpendicular to the direction of travel
Polarizing filter
- Polarizing filter it has a transmission axis and passes only the component of oscillation along it
Malus's law
- I = I0 cos2θ for an ideal filter
- I0 is the intensity of plane-polarized light incident on the filter.
- θ is the angle between its plane of polarization and the filter axis.
- Crossed filters (θ = 90°) transmit nothing.
Unpolarized light
- Unpolarized light the first filter halves the intensity and makes the light polarized, then Malus's law applies
Evidence
- Evidence only transverse waves can be polarized, which shows light is transverse and sound in air can never be polarized
Part 7 of 9Everyday cases
Glare
- Glare light reflected from water or road is partially polarized, so polarizing sunglasses reduce it
Rotation
- Rotation some crystals and solutions rotate the plane of polarization, which is used to study sugar concentration and stress in transparent plastics
Seismic waves
- P-waves are longitudinal and travel through solid and liquid, while S-waves are transverse and cannot travel through liquid
- This is how the liquid outer core of the Earth was inferred.
Part 8 of 9Transverse and longitudinal waves compared
| Feature | Transverse | Longitudinal |
|---|---|---|
| Particle motion | Perpendicular to travel | Parallel to travel |
| Pattern | Crests and troughs | Compressions and rarefactions |
| Polarization | Possible | Impossible |
| Medium | Mechanical ones need a medium resisting shear; electromagnetic ones need none | Solids, liquids and gases |
| Wave equation | v = fλ | v = fλ |
Part 9 of 9More from the specification
More from the specification
Transverse waves
- Transverse waves oscillations are perpendicular to the direction of energy travel, as in light and water waves.
Longitudinal waves
- Longitudinal waves oscillations are parallel to travel, forming compressions and rarefactions, as in sound.
Wave quantities
- Wave quantities amplitude is the maximum displacement, period is the time for one cycle, and frequency is its reciprocal in hertz.
Wave equation
- Wave equation speed equals frequency times wavelength, with wavelength measured in metres.
Electromagnetic spectrum
- Electromagnetic spectrum transverse waves from radio to gamma that share a speed in vacuum but differ in frequency range.
Frequency
- Revolutions per second, f = 1/T.What the symbols mean: T = period, the time for one complete wave (s) · f = frequency (Hz)
Period
- Time for one revolution.
Amplitude
- Maximum displacement from equilibrium.
Spectrum
- Range of colours in white light.
Equilibrium
- State with zero net force.
Equilibrium position
- Position where the net force is zero.
Electromagnetic spectrum
- Continuous family of waves from radio waves to gamma rays
Matter wave
- The wave associated with a moving particle such as an electron.
Key terms
| Term | Meaning |
|---|---|
| Transverse wave | Oscillation perpendicular to the direction of energy transfer. |
| Longitudinal wave | Oscillation parallel to the direction of energy transfer. |
| Compression | Region of higher-than-average particle density and pressure. |
| Rarefaction | Region of lower-than-average density and pressure. |
| Polarized wave | Transverse wave oscillating in one plane only. |
| Malus's law | I = I₀cos²θ for transmission through an ideal polarizer. |
Avoid these mistakes
1
Saying sound waves are transverse — air particles oscillate parallel to the travel direction.
2
Thinking longitudinal waves cannot be drawn as sine graphs — they can, but the graph plots displacement against position.
3
Using Malus's law for unpolarized light without first halving the intensity.
4
Believing polarization applies to any wave — only transverse waves can be polarized.
5
Placing the pressure maximum at the point of maximum displacement — it is at zero displacement.
Marked practiceQuizzes for this lesson
Last updated:
\n