3.4.3Waves
Effects of Sound Waves — Cambridge IGCSE Co-ordinated Sciences 0654 - Physics Revision Notes & Topical Questions
5 min read 9 parts Lesson 20 of 21
Part 1 of 7Pitch and loudness
Frequency and pitch
- Frequency and pitch high pitch means high frequency, or short wavelength, and low pitch means low frequency
Amplitude and loudness
- Amplitude and loudness large amplitude gives greater loudness and small amplitude gives lower loudness
Oscilloscope traces
- Oscilloscope traces height shows loudness and the number of waves in a given time shows pitch
Period and frequency
- Period and frequency the period T is the time for one complete wave and f = 1 ÷ T
Part 2 of 7Echoes
Echo
- Echo the reflection of a sound wave from a hard surface
Equation
- Equation distance = ½ × speed × time
- Time is the total time to the surface and back
- Speed of sound in air is 330 to 350 m/s
Why halve
- Why halve the sound travels there and back
Separate echo
- Separate echo must arrive at least about 0.1 s later, so the surface must be at least 17 m away
Reverberation
- Reverberation in small rooms the echo overlaps the original sound
Part 3 of 7Absorption and room design
Soft materials
- Soft materials curtains, carpets and foam absorb sound instead of reflecting it
Hard surfaces
- Hard surfaces reflect sound and give an echoing environment
Concert halls
- Concert halls use a mixture of reflecting and absorbing surfaces
Recording studios
- Recording studios thick absorbing walls avoid echoes
Part 4 of 7Refraction and diffraction
Refraction
- Refraction sound refracts when its speed changes, for example in layers of air at different temperatures
Diffraction
- Diffraction longer wavelengths diffract most
Low pitch
- Low pitch a 100 Hz note has a wavelength of 3.4 m and spreads widely through a doorway
High pitch
- High pitch a 5 kHz note has a wavelength of 6.8 cm and travels more like a beam
Part 5 of 7Sound on solids
Vibration
- Vibration fluctuating pressure makes a solid surface vibrate in step with the sound
Hearing
- Hearing this is how sound is detected by the ear and by a microphone
Part 6 of 7Noise and hearing safety
Hearing damage
- Hearing damage very loud sounds damage the ear, particularly over a long time
Loudness scale
- Loudness scale measured in decibels
Protection
- Protection ear defenders reduce the sound reaching the ear
Part 7 of 7More from the specification
More from the specification
Longitudinal Nature of Sound
- Sound propagates through materials as longitudinal pressure waves consisting of alternating compressions of high particle density and rarefactions of low particle density.
Ultrasound Flaw Detection
- Short ultrasonic pulses transmitted into metal components reflect from boundaries and internal crack surfaces, enabling precise fault depth determination from transit time.
Pulse-Echo Depth Measurement
- In sonar echo experiments, ultrasound pulses travel to the seabed and back;
- dividing total transit time by two and averaging multiple readings gives the accurate liquid depth.
Acoustic Reflection at Boundaries
- Partial reflection of ultrasound occurs at tissue or material boundaries with differing acoustic impedances, generating detailed diagnostic scans without ionizing radiation.
Average speed
- Total distance divided by total time.
Ultrasound
- Sound with a frequency above 20 kHz
Compression
- Decrease in length under a squashing force.
Rarefaction
- Region of a longitudinal wave where particles are spread apart
Boundary
- Surface between two media at which waves are partially reflected
Longitudinal wave
- Wave whose vibrations are parallel to the direction of travel
Independent variable
- The variable deliberately changed, here time
Dependent variable
- The variable measured, here temperature
Control variable
- A quantity kept the same to make the test fair
Key terms
| Term | Meaning |
|---|---|
| Echo | Reflection of sound from a hard surface |
| Pitch | How high or low a sound is, set by frequency |
| Loudness | How loud a sound is, set by amplitude |
| Reverberation | Overlapping of echoes with the original sound in small rooms |
| Decibel | Unit used to measure loudness |
Avoid these mistakes
1
Forgetting to halve the distance in an echo calculation — the sound travels to the surface and back.
2
Mixing up pitch and loudness — pitch is frequency and loudness is amplitude.
3
Saying a louder sound has a higher frequency — loudness depends on amplitude.
4
Reading a trace with the wrong time unit — convert milliseconds before calculating f.
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