3.1.3Waves
Transverse and Longitudinal Waves — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 9 parts Lesson 5 of 35 1 quiz
Curriculum Equation Key Wave Speed & Doppler Effect FormulasFast Exam Solution
v = f × λ | f_obs = f × (v ± v_o) / (v ∓ v_s) | T = 1 / f
Lesson summary
3.1.3 Transverse and Longitudinal Waves — IGCSE PHYSICS notes: Distinguish transverse and longitudinal waves by their direction of vibration, structure and examples.Definition — waves where the direction of vibration is at right angles to the direction of propagationParticles — v…
- Mechanical transverse waves
- Compressions
- Rarefactions
- Wavelength
- Always state the direction
- Not enough
Part 1 of 7Transverse waves
Transverse waves
Definition
- Definition waves where the direction of vibration is at right angles to the direction of propagation
Particles
- Particles vibrate perpendicular to the direction in which the wave travels
Structure
- Structure crests (peaks) and troughs
Seen in
- Seen in a rope moved quickly up and down
Examples
- Electromagnetic waves such as radio waves, visible light and X-rays
- Ripples on the surface of water
- Seismic S-waves
Mechanical transverse waves
- Mechanical transverse waves travel through solids and along liquid surfaces but not through the body of a liquid or through a gas
Non-mechanical transverse waves
- Non-mechanical transverse waves can move in a vacuum, because electromagnetic waves are oscillating electric and magnetic fields
Part 2 of 7Longitudinal waves
Longitudinal waves
Definition
- Definition waves where the direction of vibration is parallel to the direction of propagation
Particles
- Particles vibrate back and forth parallel to the direction of travel
Medium
- Medium travel in solids, liquids and gases but not in a vacuum
Compressions
- Compressions regions where the particles are close together, at high pressure
Rarefactions
- Rarefactions regions where the particles are spread apart, at low pressure
Seen in
- Seen in a slinky spring moved quickly backwards and forwards
Examples
- Sound waves
- Seismic P-waves
Wavelength
- Wavelength from the centre of one compression to the next
Part 3 of 7Comparing the two
| Property | Transverse | Longitudinal |
|---|---|---|
| Structure | Crests and troughs | Compressions and rarefactions |
| Vibration | Right angles to propagation | Parallel to propagation |
| Vacuum | Only electromagnetic waves travel | Cannot travel |
| Material | Solids and liquid surfaces | Solids, liquids and gases |
| Density | Constant | Varies |
| Pressure | Constant | Varies |
Part 4 of 7Describing the direction of vibration
Describing the direction of vibration
Always state the direction
- Always state the direction give the direction of vibration relative to the direction of wave travel
Not enough
- Not enough saying the wave travels in the direction of energy transfer is true of every wave
Seismic waves
- P-waves are longitudinal and S-waves are transverse
Part 5 of 7Demonstrations
Transverse
- Transverse a sideways jerk on a slinky makes a pulse whose coils move sideways and return
Longitudinal
- Longitudinal pushing and pulling along the slinky makes a pulse whose coils move to and fro
Sound needs a medium
- Sound needs a medium a ringing bell in a jar is heard less as air is pumped out although it is still seen vibrating
Part 6 of 7Drawing and labelling
Transverse wave
- Transverse wave label a crest, a trough, one wavelength and the amplitude
Longitudinal wave
- Longitudinal wave label a compression, a rarefaction and one wavelength
Loudspeaker
- Loudspeaker its cone moving forwards makes a compression and moving backwards makes a rarefaction
Frequency
- Frequency the source frequency gives the number of compressions per second, and so the pitch heard
Part 7 of 7More from the specification
1The Wave Speed Equation
- Wave speed v is the distance travelled by a wave per unit time, governed by the universal wave equation v = f·λ,
- where f is the frequency measured in hertz (Hz) and λ is the wavelength measured in metres;
- when a wave transitions into a medium of differing optical density, its speed and wavelength change while its frequency remains constant.
2Reflection and Refraction of Wavefronts
- When straight wavefronts encounter a flat barrier, reflection occurs such that the angle of incidence equals the angle of reflection;
- when crossing into a medium where wave speed changes, refraction alters wavefront direction, analogous to optical image formation by lenses.
3Diffraction Through Gaps and Around Obstacles
- Diffraction is the spreading of wavefronts as they pass through a gap or around an obstacle;
- maximum diffraction occurs when the gap width is comparable to the wavelength,
- producing semi-circular wavefronts while wave speed, frequency,
- and wavelength remain unchanged.
4Diffraction
- Spreading of waves through a gap or around an edge
5Wavefront
- Line joining points on a wave that are in step
6Reflection
- Light bouncing off a surface.
7Distance
- Total length of path travelled, a scalar.
8Refraction
- Change in direction of light when it changes speed between media.
9Position
- Location relative to a reference point.
10Period
- Time for one revolution.
Key terms
| Term | Meaning |
|---|---|
| Transverse wave | Wave whose vibration is at right angles to the direction of propagation |
| Longitudinal wave | Wave whose vibration is parallel to the direction of propagation |
| Compression | Region of a longitudinal wave where particles are close together |
| Rarefaction | Region of a longitudinal wave where particles are spread apart |
| Propagation | Direction in which the wave travels |
Avoid these mistakes
1
Saying a transverse wave moves in the direction of vibration — vibration is at right angles to travel.
2
Saying sound travels in a vacuum — longitudinal waves need particles.
3
Defining the type without naming the direction of vibration relative to travel — state perpendicular or parallel.
4
Mixing up P-waves and S-waves — P-waves are longitudinal and S-waves are transverse.
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