SOUND

Sound ek energy ka form hai jo humare kaano mein sunne ki sensation paida karta hai. Sound hamesha vibrating objects se produce hota hai.

• Vibration: Kisi object ka rapid to and fro motion (aage-peeche ya upar-neeche) uski mean position ke around. Jab koi object vibrate karta hai, toh woh apne aas-paas ke medium ke particles ko bhi vibrate karata hai, jisse sound produce hota hai.
• Examples of Sound Production:
• Vocal Cords: Human voice vocal cords ke vibration se banti hai.
• Musical Instruments:
• String Instruments (Guitar, Sitar): Strings ke vibration se.
• Wind Instruments (Flute, Shehnai): Air column ke vibration se.
• Percussion Instruments (Drum, Tabla): Stretched membrane ke vibration se.
• Tuning Fork: Jab iske prongs ko strike karte hain, toh woh vibrate karte hain aur sound produce karte hain.

Activity 11.1 & 11.2 ka Conclusion:

• Jab vibrating tuning fork ko touch karte hain, toh vibration feel hota hai aur sound sunai deta hai.
• Vibrating tuning fork jab water surface ko touch karta hai, toh ripples bante hain, jo show karte hain ki vibration ho raha hai.

Sound ko travel karne ke liye ek medium ki zaroorat hoti hai. Yeh vacuum mein travel nahi kar sakta.

• Medium: Woh substance ya matter jiske through sound transmit hota hai. Medium solid, liquid ya gas ho sakta hai.
• Sound as a Wave: Sound ek wave ki tarah propagate karta hai. Wave ek disturbance hai jo medium mein travel karti hai, jismein medium ke particles khud travel nahi karte, balki disturbance ko aage badhate hain.
• Mechanical Waves: Sound waves ko mechanical waves kehte hain kyunki unhe propagation ke liye ek material medium ki zaroorat hoti hai.
• Particle Motion:

1. Vibrating object apne contact mein aane wale medium particle ko displace karta hai.
2. Yeh particle adjacent particle par force lagata hai aur use displace karta hai.
3. Pehla particle apni original position par wapas aa jata hai.
4. Yeh process continue hota hai jab tak sound listener ke ear tak nahi pahunch jata.

• Important: Particles khud travel nahi karte, sirf disturbance travel karta hai.

Compressions (C) aur Rarefactions (R)

Jab koi vibrating object forward move karta hai, toh woh apne saamne ki air ko push karta hai, jisse high pressure region banta hai. Ise compression (C) kehte hain. Jab vibrating object backward move karta hai, toh woh apne peeche low pressure region banata hai. Ise rarefaction (R) kehte hain.

• Series of C and R: Object ke rapid back and forth motion se air mein compressions aur rarefactions ki ek series banti hai, jo sound wave ki tarah propagate karti hai.
• Pressure/Density Variation: Sound ka propagation medium mein pressure aur density variations ke roop mein bhi dekha ja sakta hai.
• Compression: High pressure, high density region.
• Rarefaction: Low pressure, low density region.

Longitudinal Waves

Sound waves longitudinal waves hoti hain.

• Definition: Longitudinal waves mein, medium ke particles wave propagation ki direction ke parallel oscillate karte hain.
• Slinky Analogy (Activity 11.4): Jab slinky ko push karte hain, toh usmein compressions aur rarefactions bante hain. Slinky ke particles aage-peeche move karte hain, lekin disturbance aage badhta hai.
• Transverse Waves: Iske opposite, transverse waves mein particles wave propagation ki direction ke perpendicular oscillate karte hain (e.g., water waves, light waves). Light waves mechanical waves nahi hain.

Sound wave ko describe karne ke liye kuch important characteristics hain:

1. Wavelength (\(\lambda\)):

• Do consecutive compressions (C) ya do consecutive rarefactions (R) ke beech ki distance.
• SI Unit: meter (m).

1. Frequency (\(\nu\)):

• Number of complete oscillations per unit time. Yaani, kitne compressions ya rarefactions ek fixed point se ek second mein cross karte hain.
• SI Unit: Hertz (Hz). (1 Hz = 1 oscillation per second).
• Frequency source ke vibration ki speed par depend karti hai. Faster vibration = higher frequency.

1. Time Period (T):

• Ek complete oscillation ko pura karne mein laga time. Yaani, do consecutive compressions ya rarefactions ko ek fixed point se cross karne mein laga time.
• SI Unit: second (s).
• Relation: \(\nu = 1/T\) ya \(T = 1/\nu\).

1. Amplitude (A):

• Medium mein mean value se particles ka maximum displacement ya disturbance.
• Sound ke liye, iski unit density ya pressure ki unit hoti hai.
• Amplitude sound ki loudness ya softness determine karta hai. Higher amplitude = louder sound.

1. Pitch:

• Yeh woh characteristic hai jisse brain sound ki frequency ko interpret karta hai.
• High frequency = High pitch (shrill sound, e.g., mosquito buzz).
• Low frequency = Low pitch (flat sound, e.g., lion's roar).
• Fig. 11.7 mein dekho, low pitch sound mein kam waves hoti hain aur high pitch mein zyada waves.

1. Loudness:

• Yeh sound ki intensity par depend karta hai. Intensity sound energy per unit area per unit time hoti hai.
• Loudness directly amplitude par depend karti hai. Larger amplitude = louder sound (Fig. 11.8).
• Sound source se door jaane par amplitude aur loudness dono decrease hote hain.

1. Quality or Timbre:

• Yeh woh characteristic hai jo same pitch aur loudness wale do sounds ko distinguish karne mein help karti hai.
• Pleasant sound ko 'rich quality' ka kehte hain.

1. Tone vs. Note:

• Tone: Single frequency ka sound.
• Note: Several frequencies ka mixture, jo sunne mein pleasant hota hai.
• Noise unpleasant hota hai.

Speed of Sound (v)

• Speed of sound (v) woh distance hai jo wave ka ek point (e.g., compression) unit time mein travel karta hai.
• Formula: \(v = \frac{Distance}{Time} = \frac{\lambda}{T}\)
• Since \(\frac{1}{T} = \nu\), toh \(v = \lambda \nu\).
• Important: Given medium mein same physical conditions par, sound ki speed almost sabhi frequencies ke liye same rehti hai.

Graphical Representation (Fig. 11.6):

• Wave ke peak ko crest aur valley ko trough kehte hain.
• Crest high compression/pressure ko represent karta hai, trough low rarefaction/pressure ko.

Sound ki speed finite hoti hai, matlab yeh ek particular speed se travel karta hai. Light ki speed se bahut kam hoti hai.

• Medium par Dependence: Sound ki speed us medium ki properties par depend karti hai jismein woh travel kar raha hai.
• Solids > Liquids > Gases: Sound ki speed generally solids mein sabse zyada, phir liquids mein, aur gases mein sabse kam hoti hai.
• Reason: Solids mein particles tightly packed hote hain, jisse vibrations jaldi transmit hote hain.
• Temperature par Dependence: Medium ka temperature badhane par sound ki speed badhti hai.
• Example: Air mein sound ki speed \(0^\circ C\) par \(331 \text{ m/s}\) aur \(22^\circ C\) par \(344 \text{ m/s}\) hoti hai.

Table: Speed of Sound in different media (at \(25^\circ C\)) | State | Substance | Speed in m/s | | :------ | :---------------- | :----------- | | Solids | Aluminium | 6420 | | Solids | Nickel | 6040 | | Solids | Steel | 5960 | | Solids | Iron | 5950 | | Liquids | Water (Sea) | 1531 | | Liquids | Water (distilled) | 1498 | | Gases | Hydrogen | 1284 | | Gases | Air | 346 | | Gases | Oxygen | 316 |

• Thunder and Lightning: Flash of light pehle dikhta hai aur thunder baad mein sunai deta hai, kyunki light ki speed sound ki speed se bahut zyada hoti hai.

Light ki tarah, sound bhi solid ya liquid surface se reflect hota hai. Reflection ke laws sound par bhi apply hote hain.

• Laws of Reflection of Sound:

1. Incident sound wave, reflected sound wave, aur reflecting surface par draw kiya gaya normal ek hi plane mein hote hain.
2. Angle of incidence (\(i\)) angle of reflection (\(r\)) ke barabar hota hai (\(\angle i = \angle r\)).

• Requirement for Reflection: Sound ke reflection ke liye ek large size ka obstacle chahiye hota hai, jo polished ya rough ho sakta hai.
• Activity 11.5: Pipes ka use karke sound reflection ko demonstrate kiya ja sakta hai. Clock ki ticking sound ko ek pipe se sunte hain aur dusre pipe ko adjust karte hain. Jab sound clear sunai deta hai, tab \(\angle i = \angle r\) hota hai.

Echo (Pratidhvani)

• Definition: Reflected sound jo original sound ke thodi der baad sunai deta hai.
• Distinct Echo ke liye Conditions:
• Human brain mein sound ki sensation lagbhag 0.1 second tak rehti hai.
• Distinct echo sunne ke liye, original sound aur reflected sound ke beech ka time interval kam se kam 0.1 second hona chahiye.
• Agar air mein sound ki speed \(344 \text{ m/s}\) hai (at \(22^\circ C\)), toh sound ko obstacle tak jaakar wapas aane mein \(0.1 \text{ s}\) lagne chahiye.
• Total distance covered = Speed \(\times\) Time = \(344 \text{ m/s} \times 0.1 \text{ s} = 34.4 \text{ m}\).
• Iska matlab, obstacle ki minimum distance source se \(34.4 \text{ m} / 2 = 17.2 \text{ m}\) honi chahiye.
• Multiple Echoes: Kabhi-kabhi multiple reflections ki wajah se ek se zyada echoes sunai de sakte hain (e.g., pahadon mein, ya bade halls mein).
• Rolling of Thunder: Yeh clouds aur land se sound ke successive reflections ki wajah se hota hai.

Reverberation (Anugoonj)

• Definition: Ek bade hall mein sound ka repeated reflection jo sound ko sunai dene tak banaye rakhta hai.
• Cause: Walls, ceiling, aur floor se sound ka multiple reflection.
• Undesirable Reverberation: Bade auditoriums ya concert halls mein excessive reverberation sound ko unclear bana deta hai.
• Reduction of Reverberation:
• Auditorium ki walls aur roof ko sound-absorbent materials (e.g., compressed fibreboard, rough plaster, draperies) se cover karte hain.
• Seats bhi sound absorbing properties wali material se banate hain.

Sound ke multiple reflection ka use kai practical situations mein hota hai:

1. Megaphones, Loudhailers, Horns, Musical Instruments (Trumpet, Shehnai):

• Yeh instruments sound ko ek particular direction mein focus karne ke liye design kiye jaate hain, taaki sound zyada door tak travel kar sake.
• Inmein conical opening hoti hai jo sound waves ko successively reflect karke aage ki taraf guide karti hai.
• [IMAGE: TODO: Megaphone and Horn diagram]

1. Stethoscope:

• Medical instrument jo body ke andar ke sounds (e.g., heartbeat, lung sounds) sunne ke liye use hota hai.
• Patient ke body se nikla sound stethoscope ki tube mein multiple reflections ke through doctor ke kaano tak pahunchta hai.
• [IMAGE: TODO: Stethoscope diagram]

1. Concert Halls, Conference Halls, Cinema Halls ki Curved Ceilings:

• In halls ki ceilings ko curved banate hain taaki sound reflect hokar hall ke sabhi corners tak evenly pahunche.
• Kabhi-kabhi stage ke peeche curved soundboard bhi lagate hain jo sound ko reflect karke audience mein evenly spread karta hai.
• [IMAGE: TODO: Curved ceiling and soundboard diagrams]

Human beings aur animals ki sound sunne ki frequency range alag-alag hoti hai.

• Audible Range for Humans:
• Average human ear ke liye sound ki audible range 20 Hz se 20,000 Hz (20 kHz) tak hoti hai.
• Children (5 saal se kam) aur kuch animals (jaise dogs) \(25 \text{ kHz}\) tak sun sakte hain.
• Age ke saath, higher frequencies sunne ki capability kam ho jaati hai.

• Infrasound (Infrasonic Sound):
• Frequencies below 20 Hz wale sounds ko infrasound kehte hain.
• Examples:
• Pendulum ka vibration (agar sun sakte toh).
• Rhinoceroses \(5 \text{ Hz}\) tak ki frequency par communicate karte hain.
• Whales aur elephants bhi infrasound range mein sound produce karte hain.
• Earthquakes se pehle low-frequency infrasound produce hota hai jo animals ko alert karta hai.

• Ultrasound (Ultrasonic Sound):
• Frequencies higher than 20 kHz wale sounds ko ultrasound kehte hain.
• Examples:
• Dolphins, bats, aur porpoises ultrasound produce karte hain.
• Bats ultrasound ka use karke apne prey ko locate karte hain (echolocation).
• Moths bats ke ultrasound ko detect kar sakte hain.
• Rats bhi ultrasound produce karte hain.

Ultrasound high frequency waves hoti hain jo obstacles ke presence mein bhi well-defined paths par travel kar sakti hain. Inka use industries aur medical purposes mein extensively hota hai.

1. Cleaning:

• Hard-to-reach parts (e.g., spiral tubes, electronic components) ko clean karne ke liye use hota hai.
• Objects ko cleaning solution mein rakhte hain aur ultrasonic waves bhejte hain.
• High frequency ki wajah se dust, grease, aur dirt particles detach hokar gir jaate hain.

1. Detecting Flaws in Metal Blocks:

• Metal blocks mein cracks ya flaws (jo bahar se invisible hote hain) ko detect karne ke liye use hota hai.
• Ultrasonic waves ko metal block se pass karte hain. Agar koi defect hota hai, toh waves reflect hokar wapas aa jaati hain, jisse flaw ka pata chalta hai.
• Ordinary sound waves iske liye use nahi kar sakte kyunki woh defects ke corners se bend ho jaati hain.
• [IMAGE: TODO: Ultrasound flaw detection diagram]

1. Medical Applications:

• Echocardiography: Heart ke different parts se ultrasonic waves ko reflect karake heart ki image banate hain.
• Ultrasonography: Internal organs (liver, gall bladder, uterus, kidney, etc.) ki images banane ke liye use hota hai.
• Body tissues mein density change hone par waves reflect hoti hain.
• Yeh waves electrical signals mein convert hoti hain aur monitor par images generate karti hain.
• Abnormalities (stones, tumors) detect karne mein help karta hai.
• Pregnancy mein foetus ki examination ke liye bhi use hota hai (congenital defects aur growth abnormalities).
• Kidney Stones: Small kidney stones ko fine grains mein break karne ke liye use hota hai, jo baad mein urine ke through flush out ho jaate hain.

1. SONAR (Sound Navigation And Ranging):

• Submarines, ships mein use hota hai underwater objects (e.g., enemy submarines, icebergs, sunken ships) ki distance, direction, aur speed measure karne ke liye.
• Ultrasonic waves ko ship se send karte hain, woh object se reflect hokar wapas aati hain.
• Time taken aur speed of sound in water ka use karke distance calculate karte hain.
• \(2d = v \times t\) (jahan \(d\) object ki distance hai, \(v\) sound ki speed, \(t\) time taken).