Sound
Introduction to Sound
Sound is a form of energy that produces the sensation of hearing in our ears. It is produced by vibrating objects and travels through a medium in the form of waves.
Sound: Sound is a form of energy which produces a sensation of hearing in our ears.
Key Points:
- Produced by vibrating objects
- Travels as a wave through medium
- Requires a medium (solid, liquid, or gas)
- Cannot travel through vacuum
- Detected by our ears
Production of Sound
Sound is produced by vibrating objects.
When an object vibrates, it causes the surrounding medium (air, water, etc.) to vibrate. These vibrations propagate through the medium and reach our ears as sound.
Examples of Sound Production:
- Vibrating string: Guitar, violin, sitar strings vibrate when plucked
- Vibrating membrane: Drum, tabla when struck
- Vibrating column of air: Flute, trumpet, pipe organs
- Vibrating vocal cords: Human speech and singing
- Vibrating objects: Tuning fork, bell, buzzer
Propagation of Sound
Sound needs a medium to travel.
Sound can travel through:
- Solids: Fastest (high density, tightly packed particles)
- Liquids: Moderate speed
- Gases: Slowest (low density, loosely packed particles)
Sound CANNOT travel through vacuum (no particles to vibrate)
Sound Waves
Sound Wave: A sound wave is a longitudinal wave in which particles of the medium vibrate parallel to the direction of wave propagation.
Longitudinal Wave Characteristics:
- Particles vibrate parallel to wave direction
- Consists of compressions and rarefactions
- Compression: Region of high pressure (particles close together)
- Rarefaction: Region of low pressure (particles far apart)
Characteristics of Sound Waves
1. WAVELENGTH (ฮป):
Distance between two consecutive compressions or two consecutive rarefactions.
SI Unit: meter (m)
2. FREQUENCY (ฮฝ):
Number of oscillations (vibrations) per second.
SI Unit: Hertz (Hz)
1 Hz = 1 vibration per second
3. TIME PERIOD (T):
Time taken to complete one oscillation.
SI Unit: second (s)
Relationship: T = 1/ฮฝ
4. AMPLITUDE (A):
Maximum displacement of particles from mean position.
Determines loudness of sound.
SI Unit: meter (m)
5. SPEED (v):
Distance traveled by sound wave per unit time.
Formula: v = ฮฝ ร ฮป
SI Unit: meter per second (m/s)
Distance between two consecutive compressions or two consecutive rarefactions.
SI Unit: meter (m)
2. FREQUENCY (ฮฝ):
Number of oscillations (vibrations) per second.
SI Unit: Hertz (Hz)
1 Hz = 1 vibration per second
3. TIME PERIOD (T):
Time taken to complete one oscillation.
SI Unit: second (s)
Relationship: T = 1/ฮฝ
4. AMPLITUDE (A):
Maximum displacement of particles from mean position.
Determines loudness of sound.
SI Unit: meter (m)
5. SPEED (v):
Distance traveled by sound wave per unit time.
Formula: v = ฮฝ ร ฮป
SI Unit: meter per second (m/s)
Speed of Sound
Speed of sound in different media at 25ยฐC:
- Air: 346 m/s (approximately 340 m/s or 330 m/s at 0ยฐC)
- Water: 1498 m/s
- Steel: 5960 m/s
- Iron: 5130 m/s
- Aluminum: 6420 m/s
Factors affecting speed:
- Nature of medium (solid > liquid > gas)
- Temperature (increases with temperature)
- Density and elasticity of medium
Reflection of Sound
Laws of Reflection of Sound:
Similar to light, sound also follows laws of reflection:
- Angle of incidence = Angle of reflection
- Incident ray, reflected ray, and normal lie in the same plane
Echo
Echo: The phenomenon of hearing our own sound after reflection from a distant object (like a hill or wall) is called echo.
Conditions for hearing an echo:
1. Minimum distance from reflecting surface = 17.2 meters
(This is because human ear can distinguish two sounds if time gap โฅ 0.1 second)
Calculation:
Distance = Speed ร Time
Total distance (to and fro) = 344 ร 0.1 = 34.4 m
Minimum distance = 34.4/2 = 17.2 m
2. Size of obstacle should be large
3. Distance should be appropriate
1. Minimum distance from reflecting surface = 17.2 meters
(This is because human ear can distinguish two sounds if time gap โฅ 0.1 second)
Calculation:
Distance = Speed ร Time
Total distance (to and fro) = 344 ร 0.1 = 34.4 m
Minimum distance = 34.4/2 = 17.2 m
2. Size of obstacle should be large
3. Distance should be appropriate
Applications of Reflection of Sound
- Megaphone: Uses multiple reflections to direct sound
- Stethoscope: Multiple reflections carry heartbeat sounds
- Hearing aid: Concentrates sound using reflection
- Sound boards: In auditoriums to spread sound uniformly
- Curved roofs: In concert halls for better acoustics
Range of Hearing
Audible Range (for humans): 20 Hz to 20,000 Hz (20 kHz)
Sounds below 20 Hz: INFRASOUND (Infrasonic)
- Cannot be heard by humans
- Examples: Earthquake, volcano, elephant calls, whale songs
- Can be heard by some animals (elephants, whales, hippos)
Sounds above 20,000 Hz: ULTRASOUND (Ultrasonic)
- Cannot be heard by humans
- Examples: Dog whistle, bat calls, dolphin communication
- Can be heard by dogs, cats, bats, dolphins
Applications of Ultrasound
Medical Applications:
- Ultrasound imaging: To see internal organs, fetus in pregnancy
- Breaking kidney stones: Lithotripsy
- Cleaning: Removing dirt from delicate instruments
- Therapy: Treating muscle pain
Industrial Applications:
- Detecting flaws: In metal blocks, railway tracks
- Cleaning: Hard-to-reach parts of machinery
- Measuring thickness: Of metal sheets
Other Applications:
- SONAR: Navigation, detecting submarines, fish finding
- Echolocation: Bats, dolphins use to navigate
SONAR (Sound Navigation and Ranging)
SONAR: A device that uses ultrasonic waves to measure distance, direction, and speed of underwater objects.
Working Principle:
- Transmitter produces ultrasonic waves
- Waves travel through water
- Reflect from object (submarine, fish, seabed)
- Receiver detects reflected waves
- Calculate distance using: d = (v ร t)/2
Where: d = distance, v = speed of sound in water, t = time for echo
Applications of SONAR:
- Measuring depth of sea (bathymetry)
- Locating underwater objects (submarines, shipwrecks)
- Detecting schools of fish
- Navigation of ships
- Underwater communication
Human Ear
Structure of Human Ear:
1. Outer Ear:
- Pinna: Collects sound waves
- Auditory canal: Carries sound to eardrum
2. Middle Ear:
- Eardrum (Tympanic membrane): Thin membrane that vibrates
- Three bones (Ossicles): Hammer, Anvil, Stirrup - amplify vibrations
3. Inner Ear:
- Cochlea: Spiral structure with fluid and hair cells
- Converts vibrations to electrical signals
- Signals sent to brain via auditory nerve
Important Formulas
1. Wave Speed: v = ฮฝ ร ฮป
Where: v = speed, ฮฝ = frequency, ฮป = wavelength
2. Frequency and Time Period: ฮฝ = 1/T or T = 1/ฮฝ
3. Distance for Echo:
2d = v ร t
d = (v ร t)/2
Where: d = distance from obstacle, v = speed of sound, t = time for echo
4. SONAR Distance:
Distance to object = (Speed of sound in water ร Time taken for echo)/2
Where: v = speed, ฮฝ = frequency, ฮป = wavelength
2. Frequency and Time Period: ฮฝ = 1/T or T = 1/ฮฝ
3. Distance for Echo:
2d = v ร t
d = (v ร t)/2
Where: d = distance from obstacle, v = speed of sound, t = time for echo
4. SONAR Distance:
Distance to object = (Speed of sound in water ร Time taken for echo)/2
Multiple Choice Questions (MCQ)
Subjective Questions
Practice these questions to strengthen your understanding. Write your answers in the space provided.