3.4Waves
Sound — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
10 min read 24 parts Lesson 31 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
3.4 Sound — IGCSE PHYSICS notes: Describe sound waves, their speed, pitch and loudness, echoes and ultrasound.Production — sound waves are produced by vibrating sourcesType — longitudinal waves of compressions and rarefactionsMedium — a medium is needed, so sound cannot travel th…
- Pressure wave
- In liquids
- Hearing range
- Definition
- Direct method
- Electronic method
Part 1 of 7Sound waves
Sound waves
Production
- Production sound waves are produced by vibrating sources
Type
- Type longitudinal waves of compressions and rarefactions
Medium
- Medium a medium is needed, so sound cannot travel through a vacuum
Pressure wave
- Pressure wave the compressions and rarefactions are changes in air pressure that vary with time
Part 2 of 7Speed of sound
In air
- 330 to 350 m/s, increasing as the air gets warmer
In liquids
- In liquids about 1500 m/s
In solids
- In solids about 5000 m/s
Order
- Order fastest in solids, slowest in gases
Part 3 of 7Pitch and loudness
Frequency
- Frequency high frequency gives a high pitch and low frequency gives a low pitch
Amplitude
- Amplitude large amplitude gives a louder sound and small amplitude gives a quieter sound
Hearing range
- Hearing range about 20 Hz to 20 000 Hz, reducing with age
Part 4 of 7Echoes
Echo
- Echo a reflection of sound from a hard surface
Distance
- Distance distance to the surface = ½ × speed × time, with the time for the sound to go and return
Part 5 of 7Ultrasound
Definition
- Definition sound with a frequency higher than 20 kHz
Uses
- Uses non-destructive testing of materials, medical scanning of soft tissue and sonar
Depth
- Depth depth = ½ × speed × time
Part 6 of 7Measuring the speed of sound
Direct method
- Direct method time sound over a long distance with wooden blocks and a stopwatch
Electronic method
- Electronic method use two microphones and an oscilloscope to find the time difference
Calculation
- Calculation speed = distance ÷ time
Part 7 of 7More from the specification
1Sound waves
- Sound is a longitudinal wave of compressions and rarefactions that needs a medium and cannot travel through a vacuum.
2Speed of sound
- Speed equals distance divided by time;
- in air it is roughly 330 to 340 m/s, and it is greater in liquids and solids.
3Measuring the speed
- Time an echo or a distant crack of a starting gun over a long distance, repeat, and take the average to reduce error.
4Frequency and pitch
- The equation v = f x wavelength links the quantities;
- higher frequency sounds have higher pitch, larger amplitude means louder.
5Ultrasound and hearing
- Human hearing spans about 20 Hz to 20 kHz;
- frequencies above that are ultrasound, used in measuring and imaging.
6Independent variable
- The variable deliberately changed, here time
7Dependent variable
- The variable measured, here temperature
8Control variable
- A quantity kept the same to make the test fair
9Average speed
- Total distance divided by total time.
10Boundary
- Surface between two media at which waves are partially reflected
Key terms
| Term | Meaning |
|---|---|
| Longitudinal wave | Wave whose vibrations are parallel to the direction of travel |
| Pitch | How high or low a sound is, set by its frequency |
| Loudness | How loud a sound is, set by its amplitude |
| Echo | Reflection of sound from a hard surface |
| Ultrasound | Sound with a frequency above 20 kHz |
Avoid these mistakes
1
Saying sound travels in a vacuum — it needs a medium.
2
Saying sound is fastest in gases — it is fastest in solids.
3
Mixing pitch and loudness — pitch depends on frequency and loudness on amplitude.
4
Forgetting the halving in echo calculations — the sound travels there and back.
Marked practiceQuizzes for this lesson
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