Sound and Hearing

• Waves are a way of transferring energy from one place to another.

Transverse and Longitudinal Waves

• In transverse waves, particles vibrate perpendicular to wave direction, like light waves.
• In longitudinal waves, particles vibrate parallel to wave direction, like sound waves.

Sound Wave Mediums

• Sound waves require a medium to travel and cannot travel in a vacuum.
• The speed of sound changes depending on the medium.
• Sound moves fastest through solids, then liquids, and slowest through gases.
• The average speed of sound in the air is 330 m/s.
• Sound moves faster through hot air than cold air.

Sound Wave Characteristics

• Amplitude: The distance from the center of the wave to the highest or lowest point.
• Wavelength: The distance between a point on one wave to the same point on the next wave.
• Frequency (Hz): The number of waves per second; f = 1/T.
• Time period (T): The time it takes for one wave.
• Low-frequency waves have a longer time period.

Loudness vs. Pitch

• Loudness is how loud or soft a sound is, depending on the amplitude of a wave.
• Higher amplitude sound waves are louder, and lower amplitude ones are quieter.
• Pitch tells how shrill or deep a sound is, depending on the frequency of a wave.
• Higher frequency sound waves have a higher pitch, and lower frequency waves have a lower pitch.

Detecting Sound

• In the ear, sound waves enter the ear canal, causing the eardrum to vibrate which amplifies the vibrations via tiny bones.
• These vibrations pass through liquid in the cochlea, where tiny hairs convert the vibration into an electrical signal, and impulses travel via the auditory nerve.
• Microphones work similarly to the inner ear.
• Sound waves move the diaphragm, and the magnetic coil makes electrical signals.
• Signals are carried through wires, and an amplifier makes the sound louder through speakers.

Audible Range and Ultrasound

• Ultrasound waves are acoustic waves greater than 20 kHz.
• Audible frequency range is approximately 20 Hz - 20 kHz.
• This range narrows as humans age.

Intensity and Decibels

• Sound intensity measures using a sound-level meter on a decibel (dB) scale.
• Higher the intensity, the louder the sound

High-Intensity Sound Dangers

• Loud sound can damage hearing and burst the eardrum.
• The level of danger depends on the sound's intensity (dB) and exposure time.

Reducing Risk of High-Intensity Sound

• High noise levels require the use of ear protectors.

Sound Wave Interference

• Interference occurs when two waves interact, adding up or cancelling each other.
• Constructive interference: waves are in step; peaks are in the same spot; total sound is louder.
• Destructive interference: waves are out of step; peaks and troughs align; total sound is quieter or silent.
• Noise cancellation works by cancelling out unwanted sound

Echoes & Reflection

• When sound hits a hard surface, it reflects off, creating an echo.
• Sound's slow travel speed creates a delay between the shout and the echo.
• The angle of incidence equals the angle of reflection for sound waves.
• Echoes are undesirable in cinemas.

Applications

• SONAR (Sound Navigation and Ranging ) is measured using: Distance = Speed x Time.
• Bats use echolocation to find the distance to objects.
• Ultrasound transmits waves, reflects at boundaries between tissues and bone, and detects echoes to construct 3D images for baby scans.