Sound wave

Study Notes

Sound Waves

Sound waves are longitudinal waves, created by vibrating particles.
Sound waves cannot travel in a vacuum (e.g., outer space).
Sound waves cause compressions and rarefactions in the medium through which they travel.
Compressions are regions of higher pressure, and rarefactions are regions of lower pressure.
Medium particles oscillate back and forth as compressions and rarefactions pass through.
When a compression passes, pressure rises; when a rarefaction passes, pressure falls.
Sound wave properties include:
- Loudness: determined by amplitude, greater amplitude = louder sound.
- Pitch: determined by frequency, higher frequency = higher pitch.
- Timbre: the quality that distinguishes one sound from another, even if they have the same frequency.
Speed of sound: determined by medium—solids > liquids > gases.
Speed of sound (v) = frequency (f) × wavelength (λ)
Examples of sound speeds in different mediums:
- Rubber: 60 m/s
- Air (0°C): 332 m/s
- Air (20°C): 343 m/s
- Air (40°C): 355 m/s
- Lead: 1210 m/s
- Gold: 3240 m/s
- Glass: 4540 m/s
- Copper: 4600 m/s
- Aluminium: 6320 m/s
Human hearing range: 20 Hz to 20 kHz.
Frequencies above 20 kHz are called ultrasonic, below 20 Hz are called infrasonic.
Measuring speed of sound—a method involves timing the interval between seeing the smoke from a gun being fired and hearing the sound of the gun shot and using the formula v=2d/t where v=speed, d=distance to the target, t=time taken.
Measuring speed of sound using equipment—signal generator, speaker, microphones and oscilloscope, set up with microphones spaced apart by one wavelength.

Uses of Ultrasound

Ultrasonic cleaning: used to clean objects by using high-frequency sound waves to dislodge dirt and debris.
Echo-sounding: used to measure the depth of bodies of water by sending sound waves into the water and measuring the time it takes for the waves to return after bouncing off the bottom.
Metal testing: used to detect flaws or defects within materials by measuring the time it takes for sound waves to return after being reflected off the flaws.
Scanning: used in medical imaging to visualize internal structures by using sound waves to create images.

True or False Statements

Sound is a longitudinal wave*: True
Sound is the vibration of matter*: True
The longer the wavelength of the wave, the higher the pitch*: False
Sound can travel in outer space*: False
Amplitude of sound corresponds to how much the wave is compressed*: True
The unit of frequency is Hertz*: True
Small obstacles cannot cause diffraction of wave*: False
Speed of sound depends on pressure of air*: True
Sound wave with higher frequency moving faster*: True
Different instruments have different qualities of sound (timbre):* True
Audio sound frequency range is 2 Hz to 2000 Hz*: False (Correct range is 20 Hz to 20,000 Hz)