Sound and Waves in Physics

Sound

• Sound is a form of energy that creates a sensation of hearing in our ears.
• Sound is produced by vibrations of objects.
• Sound travels in the form of waves.

Production of Sound

• Sound is created by vibrating objects.

• Vibrations produce compressions and rarefactions in the surrounding air.

• These compressions and rarefactions form sound waves.

• Energy from an external source (like a hand, wind) is needed to make an object vibrate and produce sound.

• Examples of sound production:

  • Vocal cords vibrating to create voice
  • Drum membrane vibrating when struck.

• Methods for producing sound:

  • Vibrating strings (sitar)
  • Vibrating air (flute)
  • Vibrating membranes (tabla, drum)
  • Vibrating plates (bicycle bell)
  • Friction
  • Scratching/rubbing objects

Propagation of Sound

• Sound needs a medium (solid, liquid, or gas) for transmission.

• Air is the most common medium for sound propagation.

• A wave is a disturbance that travels through a medium, causing neighboring particles to move.

• Sound waves are mechanical waves.

• Sound waves create compressions (high-pressure regions) and rarefactions (low-pressure regions) in the medium.

• Compressions and rarefactions move away from the source.

• Sound needs a medium to propagate.

• Sound cannot travel in a vacuum

Sound Waves as Longitudinal Waves

• Sound waves are longitudinal waves.
• The medium's particles vibrate parallel to the direction of wave propagation.
• Longitudinal waves involve compressions and rarefactions.

Characteristics of Sound Waves

• Wavelength (λ): The distance between two consecutive compressions or rarefactions. Measured in meters (m).
• Frequency (f): The number of complete oscillations (compressions/rarefactions) per unit time. Measured in Hertz (Hz).
• Amplitude (A): The maximum displacement of a particle from its undisturbed position. Measured in meters (m).

Time Period (T)

• Time taken for one complete oscillation.
• Inversely related to frequency (f = 1/T).
• Measured in seconds (s).

Relationship between Frequency and Time Period

• Frequency equals one divided by the time period.

Pitch

• Pitch depends on the frequency of the sound.
• Higher frequencies mean higher pitch.
• Lower frequencies mean lower pitch.

Timbre

• The quality or characteristic of a sound, even if it has the same pitch and amplitude.

Loudness

• Loudness depends on the amplitude of a sound wave.
• Higher amplitude means louder sound.

Velocity

• Speed of sound dependent on medium. Measured in meters per second (m/s).
• Velocity equals frequency multiplied by wavelength.

Speed of Sound in Various Mediums

• Speed of sound varies depending on the medium's density and temperature.
• Sound travels fastest in solids, slower in liquids and slowest in gases.
• Higher temperatures typically increase sound speed.

Sonic Boom

• Occurs when an object travels faster than the speed of sound.
• Produces shock waves.

Reflection of Sound

• Sounds reflect off hard surfaces.
  • Angle of incidence equals angle of reflection.
• Echo: Repetition of sound due to reflection.
• Minimum time interval for echo to be heard is 0.1s for distinct echo.
• Reverberation: Persistence of sound in a large hall due to multiple reflections.
• Methods to reduce reverberation: heavy curtains, carpets, sound-absorbing materials.

Applications of Reflection of Sound

• Megaphones
• Loudspeakers
• Stethoscopes
• Sound boards
• Curved ceilings in concert halls
• Reflection from hard surfaces creates an echo

Range of Hearing

• Humans hear sounds between 20Hz and 20,000Hz.
• Animals have different ranges of hearing.
• Infrasonic sound: below 20Hz.
• Ultrasonic sound: above 20,000Hz.

Applications of Ultrasound

• Detecting cracks in metals
• Cleaning hard-to-reach objects
• Examining internal organs (echocardiography, ultrasonography)
• Breaking up kidney stones

Sonar

• Used to find underwater objects.
• Uses ultrasonic waves to measure distance, direction, and speed.
• SONAR consists of a transmitter and detector installed on the ship.

Structure of the Human Ear

• Outer ear (pinna, auditory canal) gathers sound waves.
• Middle ear (eardrum, hammer, anvil, stirrup) amplifies vibrations.
• Inner ear (cochlea) converts vibrations to electrical signals.
• Electrical signals are sent to brain via auditory nerve to interpret sound.