3.1Waves
General Properties OF Waves — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
15 min read 30 parts Lesson 2 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 General Properties of Waves — IGCSE PHYSICS notes: Describe waves, their features, the wave equation, transverse and longitudinal waves and reflection, refraction and diffraction.Energy transfer — waves transfer energy without transferring matterOscillation — the medium vibra…
- Wavelength
- What the symbols mean
- Crest and trough
- Wave speed
- Both wave types
- Unit conversions
Part 1 of 7Waves and energy
Energy transfer
- Energy transfer waves transfer energy without transferring matter
Oscillation
- Oscillation the medium vibrates about a fixed point, for example water ripples move particles up and down and sound moves air back and forth
Evidence
- Evidence a floating object bobs up and down but does not travel with the wave
Part 2 of 7Features of a wave
Features of a wave
Amplitude
- Amplitude the maximum displacement of a wave from its undisturbed position, symbol A, unit m
Wavelength
- Wavelength the distance from one point on a wave to the same point on the next wave, symbol λ, unit m
Frequency
- Frequency the number of waves passing a point per second, symbol f, unit hertz (Hz)
Period
- Period the time for one complete wave to pass a point, T = 1 ÷ fWhat the symbols mean: T = period, the time for one complete wave (s) · f = frequency (Hz)
Wavefront
- Wavefront a line joining points on a wave that are in step, usually the crests
Crest and trough
- Crest and trough the highest and lowest points of a wave relative to the undisturbed position
Wave speed
- Wave speed the distance travelled by a wave each second
Part 3 of 7The wave equation
The wave equation
Equation
- Equation v = fλ, with v in m/s, f in Hz and λ in mWhat the symbols mean: v = wave speed (m s−1) · f = frequency (Hz) · λ = wavelength (m)
Both wave types
- Both wave types transverse and longitudinal waves obey the equation
Unit conversions
- Unit conversions convert cm to m by dividing by 100, kHz to Hz by multiplying by 1000 and MHz to Hz by multiplying by 1 000 000
Part 4 of 7Transverse and longitudinal waves
| Property | Transverse | Longitudinal |
|---|---|---|
| Vibration | At right angles to the direction of travel | Parallel to the direction of travel |
| Pattern | Crests and troughs | Compressions and rarefactions |
| Vacuum | Only electromagnetic waves travel through it | Cannot travel through it |
| Examples | Light, water ripples, S-waves | Sound, P-waves |
Part 5 of 7Reflection, refraction and diffraction
Reflection
- Reflection a wave bounces back at a boundary and stays in the original medium
- Angle of incidence equals angle of reflection
- Speed, wavelength and frequency are unchanged
Refraction
- Refraction a wave changes speed at a boundary between media
- Speed and wavelength change, frequency stays the same
- Slowing waves bunch together and turn towards the normal
Diffraction
- Diffraction waves spread out when they pass through a narrow gap or past an edge
- Wavelength and speed are unchanged
- Greatest when the gap width is about equal to the wavelength
Part 6 of 7Ripple tank
Purpose
- Purpose shows reflection, refraction and diffraction of water waves
Set-up
- Set-up a lamp above the tank projects the wavefronts onto a screen below
Measuring speed
- Measure the length across several wavefronts and divide by the number of waves to find λ
- Count the waves passing a point in a set time to find f
- Calculate v = fλ and repeat to average
Part 7 of 7More from the specification
1Wave
- Wave a disturbance that transfers energy from place to place without transferring matter
2Wavelength, frequency and amplitude
- Wavelength, frequency and amplitude wavelength is the distance between successive crests, frequency is waves per second in hertz, amplitude is the maximum displacement
3Wave speed equation
- Wave speed equation v = f x wavelength, with speed in metres per second
4Transverse and longitudinal waves
- Transverse and longitudinal waves particles vibrate at right angles to the direction of travel in transverse waves and parallel to it in longitudinal waves
5Refraction at a glass block
- Refraction at a glass block light bends towards the normal on entering glass because it slows down,
- and the emergent ray is parallel to the incident ray
6Wave
- Wave a disturbance that transfers energy from place to place without transferring matter
7Wavelength, frequency and amplitude
- Wavelength, frequency and amplitude wavelength is the distance between successive crests, frequency is waves per second in hertz, amplitude is the maximum displacement
8Wave speed equation
- Wave speed equation v = f x wavelength, with speed in metres per second
9Transverse and longitudinal waves
- Transverse and longitudinal waves particles vibrate at right angles to the direction of travel in transverse waves and parallel to it in longitudinal waves
10Refraction at a glass block
- Refraction at a glass block light bends towards the normal on entering glass because it slows down,
- and the emergent ray is parallel to the incident ray
Key terms
| Term | Meaning |
|---|---|
| Wavelength | Distance between a point on one wave and the same point on the next wave |
| Frequency | Number of waves passing a point per second |
| Amplitude | Maximum displacement from the undisturbed position |
| Wavefront | Line joining points on a wave that are in step |
| Diffraction | Spreading of waves through a gap or around an edge |
Avoid these mistakes
1
Saying a wave carries matter — it carries energy while the medium only oscillates.
2
Measuring amplitude from crest to trough — it is measured from the undisturbed position to a crest or trough.
3
Saying the frequency changes in refraction — frequency stays the same while speed and wavelength change.
4
Forgetting unit conversions in v = fλ — convert to m and Hz first.
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