Sound Waves: Characteristics and Applications: Class 9 Science Chapter 10 Hinglish mein

Kitchen mein pressure cooker ki seeti bajti hai, bahar auto-rickshaw horn deta hai, gali mein mandir ki ghanti bajti hai aur agle kamre se ek dost tumhara naam pukaarta hai. Bina dekhe tum jaante ho ki har ek kya hai, kyunki har ek tum tak sound ban kar pahunchta hai.

Chapter 7 mein tumne dekha ki energy kabhi kuch nahi se paida nahi hoti aur na gayab hoti hai; woh bas apna form badalti hai. Sound unhi forms mein se ek hai. Yeh chapter teen sawaal poochta hai. Kis tarah ki motion sound banati hai? Woh sound apne source se tumhare kaan tak kaise pahunchti hai? Aur hum uske baare mein kya measure kar sakte hain? Inke jawab hall mein echo, referee ki seeti ki tez awaaz aur ek ship lehron ke bahut neeche pade wreck ko kaise dhoondhta hai, yeh sab samjhaate hain.

10.1 Sound ka Production

Desk ke kinaare par dabaye steel ruler ko jhatko, steel ke glass ko chammach se thapthapao, ya khaali bottle ke munh par se phoonk maaro. Har baar koi cheez tezi se aage-peeche hilti hai, aur tumhe sound sunayi deti hai. Aisi sounds tumne apni arts classes mein banayi hain. Grade 7 mein tum sonority se bhi mile the: woh khanakti awaaz jo brass aur steel jaise metals maarne par dete hain, jaise mandir ki ghanti ya manjira ki jodi.

To sound ek vibrate karte object se banti hai, aur jo object vibrate karta hai use sound ka source kehte hain. Sources kuch families mein aate hain: kheenche hue strings (sitar, ektara), kheenchi hui skins ya membranes (tabla, dholak), hawa ke columns (bansuri, shehnai, shankh) aur solid bodies (ghanti, manjira). Zyaadatar instruments ek se zyada ka use karte hain. Sitar mein strings khokhle gourd (tumba) ko hilaate hain, aur gourd ke andar ki hawa bhi vibrate karti hai.

Apni ungliyon ke siron ko gale ke saamne halke se rakho aur gungunao: tumhe ek jhanjhanahat mehsoos hoti hai. Yeh vocal cords se aati hai, muscle ki do tahein jo tumhare voice box (larynx) ke aar-paar kheenchi hui hain. Lungs se upar aati saans unhe khulte-band hote hue vibrate karati hai. Phir tumhari jeebh, daant, honth aur munh aur naak ke khaali hisse us jhanjhanahat ko shabdon ya gaane ka roop dete hain. Insects ke paas aur tarike hain: cicada apne body par drum jaisi plates ko click karta hai, aur cricket ek pankh ke dhaaridaar kinaare ko doosre par ragadta hai.

10.1.1 Tuning fork

Music teachers aur physics labs ek hi kaam ka sound source rakhte hain: tuning fork. Steel ya aluminium ka ek capital U socho jo ek chhote handle, stem, par khada hai. Uski do bhujaon, prongs (ya tines), mein se ek ko rubber pad par thapthapao aur fork ek steady, saaf note ke saath gunj uthta hai. Har fork hamesha same note deta hai, aur uski value us par likhi hoti hai.

10.2 Sound ka Propagation

Sound ko apne source aur tumhare beech ka gap paar karna hota hai. Hawa iska seedha raasta hai. Lekin kya sound ek wooden bench se, ya paani ki balti se bhi guzar sakti hai? Do quick tests se pata chal jaata hai.

Wood, paani, hawa: sound teeno se guzar gayi. Tum tak aate hue sound jis cheez se guzarti hai, woh uska medium hai, jo matter ki koi bhi state ho sakti hai: solid, liquid ya gas.

Isse ek paheli khadi hoti hai. Agar source aur tumhare beech koi cheez hi na ho to? Jis region mein koi bhi matter na ho, woh vacuum hai. Kya sound use paar kar sakti hai?

10.2.1 Sound ko propagate hone ke liye medium chahiye

Ek battery buzzer ko airtight glass dome, yaani bell jar, ke neeche rakho, jo ek plate par khada hai aur plate vacuum pump se judi hai. Buzzer on karo: tumhe woh saaf sunayi deta hai. Ab hawa bahar pump karna shuru karo Fig. 10.3.

Fig. 10.3 ka loudness bar poori kahani batata hai. Jar mein jitne kam air particles bachte hain, ghanti utni dheemi hoti hai, phir bhi glass ke through tum hammer ko poore samay maarte dekh sakte ho. Jab lagbhag hawa nahi bachti, buzzer lagbhag chup ho jaata hai; valve kholo aur ghanti phir bajne lagti hai. Buzzer poore samay vibrate karta raha. Sirf medium badla, isliye sound ko medium chahiye, aur vacuum use nahi le jaata.

Planets ke beech ka space lagbhag perfect vacuum hai. Satellite se takraata spanner khaali space ke through paas tairte astronaut tak koi sound nahi bhejta. Lekin satellite ko chhoota astronaut metal aur suit ke through vibration mehsoos kar sakta hai. Spacewalkers apne helmets ke andar radio sets se baat karte hain: radio waves, light ki tarah, ko medium nahi chahiye. Shuru wali paheli ka bhi yahi jawab hai: Moon par lagbhag hawa nahi hai, isliye wahan bajaayi taali paanch metre door partner tak koi sound nahi bhejti.

10.3 Sound Waves

Hum jaante hain ki sound ko medium chahiye. Lekin drum aur tumhare kaan ke beech ki hawa ke saath asal mein hota kya hai? Sound source se ek saath kai directions mein nikalti hai (isiliye tuning fork har taraf se sunayi diya tha). Exact pattern source ki shape par depend karta hai. Yeh sab follow karna uljha hua hai, isliye hum simplify karte hain, jaise scientists aksar karte hain: socho ki sound ek lambe, patle pipe mein band hai, jahan woh sirf ek taraf travel kar sakti hai.

Ab slinky ki jagah ek lambi tube mein hawa lo. Tube ka ek end ek piston se band hai jo andar-bahar khisak sakta hai; doosra end khula hai. Piston hamara source ka model hai: ise side se dikhne wala loudspeaker cone samjho. Fig. 10.4 ke steps follow karo.

Tube ki hawa ko logon ki ek lambi line samjho, har koi agle se ek kadam door khada hai. Rest par har gap same hai, aur hawa ki normal, average density hai. Ab piston achaanak aage jhatka khaata hai. Hawa ki pehli layer doosri layer mein dhakel di jaati hai isse pehle ki doosri hil sake, isliye ek pal ke liye yeh particles normal se zyada paas bhar jaate hain. Aisa bhara hua region compression (C) hai. Phir doosri layer teesri ko dhakelti hai, aur teesri chauthi ko. Bhara hua region tube mein aage aise pass hota hai jaise line mein ek dhakka aage badhta hai, jabki har insaan bas thoda aage ladkhadaata hai aur wapas aa jaata hai.

Jab piston peeche hat-ta hai, to apne peeche thodi extra jagah chhod deta hai. Hawa ki sabse paas wali layer us jagah mein wapas khisakti hai, aur phir agli layer peeche aati hai. To normal se zyada chaude gaps wala ek region, ek rarefaction (R), bhi tube mein aage daudta hai.

Piston ko andar-bahar chalate raho aur woh ek ke baad ek bhare aur faile regions bhejta hai: C, R, C, R. High aur low density ka yeh travel karta pattern ek sound wave hai. Dhyaan do ki kya travel nahi karta: khud hawa. Sirf pattern chalta hai, aur woh jis direction mein chalta hai woh wave ki direction of propagation hai.

Khuli jagah mein particles ko koi cheez gher kar nahi rakhti. Har compression har taraf bahar ki taraf dhakelta hai aur source ke charon taraf ek phailta hua shell ban jaata hai, jaise phoolta hua balloon. Isliye ek chhota source compression aur rarefaction ke spherical shells bhejta hai. Jab yeh shells tumhare kaan tak pahunchte hain, tumhe sound sunayi deti hai.

Fig. 10.4 ko phir se dekho. Har particle tube ke saath aage-peeche hilta hai, usi line par jis par wave travel karti hai.

Kyunki disturbance ko aage pass karne ke liye sound ko particles chahiye, isliye woh matter ke bina exist nahi kar sakti. Is tarah ki waves ko mechanical waves kehte hain.

Mechanical waves do tarah ki hoti hain. Ek rassi ka ek end khambe se baandho aur doosre end ko upar-neeche jhatko. Rassi par ubhaar aage daudte hain, jabki rassi ka har hissa upar-neeche hilta hai, ubhaar ke travel ki direction ke right angle par. Jis wave mein particles travel ki direction ke perpendicular vibrate karte hain, woh transverse wave hai Fig. 10.5. Sound, jaisa humne dekha, ek longitudinal wave hai.

10.4 Sound Waves ki Energy

Vibrate karta source apne paas wali hawa ki layer par work karta hai. Har particle apne padosiyon se takra kar dhakka aage pass karta hai, isliye energy particle se particle tak aage di jaati hai, haalaanki koi particle khud yeh safar nahi karta. Sound wave mein energy travel karti hai, medium nahi. 11Air particles kabhi sach mein ruke nahi hote: apni thermal energy ki wajah se woh randomly idhar-udhar bhaagte rehte hain. Guzarti sound wave is random motion ke upar ek chhoti, vyavasthit aage-peeche ki motion jod deti hai, aur wave ke guzar jaane ke baad yeh extra motion khatam ho jaati hai.

10.5 Sound Wave ka Graphical Representation

Ek sound wave ko ek pal par freeze karo aur uske raaste ke points par hawa ki density measure karo. Compressions mein density average se zyada hoti hai; rarefactions mein kam. Density ko page par upar ki taraf aur source se distance ko page ke aar-paar plot karo, aur tumhe ek smooth, lehrata curve milta hai. Ek dashed horizontal line average density dikhati hai, yaani bina disturb hui hawa ki density Fig. 10.7.

Curve ki chotiyon ko, jahan density sabse zyada hoti hai, crests kehte hain; woh compressions ke centres par hoti hain. Gaddhon ko, jahan density sabse kam hoti hai, troughs kehte hain; woh rarefactions ke centres par hote hain. Crest aur trough ke beech density apni average value se guzarti hai.

Ek doosri tarah ka graph bhi utna hi kaam ka hai. Ek fixed point par khade ho jao aur samay ke saath wahan ki density record karo. Jaise-jaise compressions aur rarefactions guzarte hain, us point par density badhti aur ghatti hai, isliye density aur time ke graph ki bhi wahi lehrati shape hoti hai. Bas horizontal axis ka label badalta hai.

10.6 Sound Wave ki Characteristics

Ek sound ko doosri se compare karne ke liye humein aisi quantities chahiye jinhe hum measure kar sakein. Sound wave ko uski wavelength, frequency (aur usse juda time period), amplitude aur speed se describe kiya jaata hai.

10.6.1 Wavelength, frequency aur time period

Ek crest se agle crest tak, ya ek trough se agle trough tak ki distance wave ki wavelength hai Fig. 10.8. Ise $\lambda$ (Greek letter lambda) se likhte hain. Kyunki yeh ek length hai, iski SI unit metre (m) hai.

Ab socho ki hawa mein ek jagah ek chhota density meter laga hai, jaise pier par tide gauge. Jaise-jaise wave guzarti hai, uski reading high tak chadhti hai (compression guzar raha hai), low tak girti hai (rarefaction) aur phir chadhti hai. Reading ka har poora cycle, high se low aur wapas high, ek oscillation hai. Meter ek second mein jitne cycles dikhata hai, unhe gino aur tumhe wave ki frequency mil jaati hai, jise $\nu$ (Greek letter nu) se likhte hain. Iski unit, "per second" (${\mathrm{s}}^{-1}$), ko hertz (Hz) kehte hain.

Meter reading ka ek cycle jitni der chalta hai, woh time period hai, symbol $T,$ aur ise seconds mein measure karte hain. Agar meter har second 100 cycles poore karta hai, to har cycle second ka sauvan hissa chalta hoga. Isliye frequency aur time period ek doosre ke reciprocals hain: frequency jitni zyada, time period utna chhota.

Roz ki zyaadatar sounds, jaise awaazein, traffic ya pressure cooker, ek saath kai frequencies ka mishran hoti hain. Maara gaya tuning fork ya steady seeti lagbhag ek hi frequency ke bahut kareeb hote hain, isiliye woh experiments ke liye kaam ke hain.

10.6.2 Sound waves ka amplitude aur intensity

Do sounds ki wavelength aur frequency same ho sakti hai, phir bhi woh hawa ko kitna dabaati hain, ismein farq ho sakta hai. Density apni average value se jitna zyada se zyada door jaati hai, woh wave ka amplitude hai. Graph par yeh dashed average line ke upar crest ki oonchai, ya uske neeche trough ki gehrai hai Fig. 10.9.

Amplitude jitna bada, wave utni zyada energy le jaati hai. Tumhare grain drum ne yeh dikhaya: plate par zor ki chot ne daanon ko halki thapki se kahin zyada ooncha uchhaala, kyunki film tak kahin zyada energy pahunchi.

Ek sound kisi jagah kitni zor se pahunchti hai, yeh uski intensity se measure hota hai. Yeh woh sound energy hai jo har second ek square metre area se guzarti hai, jab woh area sound ke travel ki direction ke saamne rakha ho.

Jaise-jaise sound ek chhote source se door jaati hai, wahi energy bade aur bade spherical shells par fail jaati hai. Dugni distance par woh chaar guna area mein bant-ti hai, aur teen guni distance par nau guna area mein Fig. 10.10. Isliye door jaane par intensity tezi se girti hai, isiliye door jaate hue cheekh dheemi pad jaati hai. Isiliye mandir ki badi ghanti poore gaon mein sunayi deti hai jabki khanakti payal kuch metres mein hi kho jaati hai. Ghanti ke paas failaane ke liye shuru se hi kahin zyada energy hoti hai.

10.6.3 Sound ki Speed

Speed of sound batati hai ki compressions aur rarefactions ka pattern medium mein kitni tezi se chalta hai. Wave ka koi ek feature chuno, maan lo ek crest, aur poochho ki woh ek second mein kitna aage badhta hai.

Sound alag-alag media mein alag speeds se chalti hai. Solids mein sabse tez, liquids mein thodi dheemi, aur gases mein sabse dheemi. Paani mein yeh hawa se lagbhag chaar se paanch guna tez, aur kai solids mein pandrah se bees guna tez travel karti hai Table 10.4.

Garam, chipchipi dopahar ki hawa thandi, sookhi subah ki hawa se sound ko thoda tez le jaati hai: garmi aur nami dono speed badhaate hain. Sookhi hawa mein sound 0 °C par lagbhag $331\mathrm{m}\mathrm{/}\mathrm{s}$ aur 25 °C par lagbhag $346\mathrm{m}\mathrm{/}\mathrm{s}$ se travel karti hai, yaani har degree par lagbhag $0.6\mathrm{m}\mathrm{/}\mathrm{s}$ zyada.

Gaane ke neeche aur oonche notes tum tak saath-saath pahunchte hain, isliye hawa mein har frequency same speed se travel karti hogi. Frequency ke saath jo badalta hai woh wavelength hai: $\lambda =v\mathrm{/}\nu ,$ isliye frequency dugni karne par wavelength aadhi ho jaati hai. Fig. 10.11 mein try karo: frequency badhao aur dekho ki wavelength chhoti hoti hai jabki speed poore samay $340\mathrm{m}\mathrm{/}\mathrm{s}$ par rehti hai. Kuch porous foams aur khaas tarah se banaye gaye materials yeh rule todte hain, lekin hawa, paani aur aam solids nahi todte.

10.6.4 Sound ko hum kaise mehsoos karte hain

Sound meter aur tumhara kaan alag-alag kaam karte hain. Meter numbers batata hai (frequency, amplitude, speed) jo koi bhi padhe, same aate hain. Tumhare kaan aur dimaag experiences batate hain: teekhi ya gehri, tez ya dheemi, flute ya awaaz. Pitch aur loudness in experiences ke naam hain, aur yeh physical numbers se bas dheele taur par jude hain, kisi saaf formula se nahi Table 10.5.

Pitch humari yeh samajh hai ki sound kitni oonchi ya neechi hai. Machchhar ki bhinbhinahat aur pressure-cooker ki seeti oonchi hoti hain; saand ki dahaad aur bada dhol neeche hote hain. Frequency badhaane se pitch badhti hai, lekin kaan frequency ko ruler ki tarah measure nahi karta. Tumhare kaan ko 100 Hz se 200 Hz jaana utna hi bada kadam lagta hai jitna 1000 Hz se 2000 Hz jaana.

Phone par dost ki awaaz tum kuch had tak uski frequency se pehchaante ho. Uske gale, munh aur naak ki shape bhi maayne rakhti hai, jo instrument ki body ki tarah kaam karti hai. Teenage ki shuruaat mein ladke ki awaaz "phat-ti" hai: uske vocal cords lambe aur bhaari ho jaate hain, har second kam baar vibrate karte hain, aur uski awaaz neechi ho jaati hai.

Duniya mein maujood zyaadatar frequencies ke liye humare kaan behre hain. Ek swasth jawaan kaan sirf lagbhag 20 Hz se lagbhag 20 000 Hz (20 kHz) tak respond karta hai, yeh audible range hai; bachche aksar apne dada-dadi se oonchi tones sun lete hain. 20 Hz se neeche infrasonic sound (infrasound) hai, aur 20 kHz se upar ultrasonic sound (ultrasound) hai Fig. 10.13. Doosre jaanwar wahan sun lete hain jahan hum nahi sun sakte. Kutta "silent" seeti ki cheekh sun leta hai, bats, billiyaan aur dolphins ultrasound sunte hain, aur haathi kilometres ke jungle ke paar infrasound mein dheemi gadgadahat se ek doosre se baat karte hain.

Loudness humari yeh samajh hai ki sound kitni zordaar hai, aur yeh amplitude ke saath chalti hai. Cheekh density mein bade jhool banati hai aur tez sunayi deti hai, phusphusahat chhote jhool banati hai aur dheemi sunayi deti hai. Loudspeaker se door jao to woh dheema lagta hai, kyunki tum tak kam intensity pahunchti hai. Intensity aur loudness jude hain lekin ek hi cheez nahi hain. Ek jagah khade do logon tak same intensity pahunchti hai, phir bhi jiski sunne ki shakti kamzor hai use sound kam tez lagti hai.

Sirf ek frequency wali sound, jaise tuning fork ya phone ki test beep, ek tone hai. Asli music zyada bhara hua hota hai. Gaane wale ka gaaya ya harmonium par bajaaya note ek sabse neechi frequency, fundamental, ko oonchi frequencies ke saath milata hai jinhe overtones kehte hain. Isliye uske graph ki shape zyada ubad-khabad hoti hai jo phir bhi dohraati hai Fig. 10.14. Sitar ise aur aage le jaata hai: uske main strings ke neeche extra strings (taraf) hote hain jo kabhi chhede nahi jaate lekin saath-saath gunjte hain aur mix ko gaadha karte hain.

Ek hi note ko violin, shehnai aur harmonium par barabar tez bajta suno, aur tum aankhein band karke bhi har instrument ka naam bata sakte ho. Character ke is farq ko timbre (bolo "tam-ber") kehte hain. Yeh is par depend karta hai ki kaun se overtones maujood hain aur har ek kitna strong hai, aur yeh instrument ki shape, material aur banawat par depend karta hai. Do notes jinki fundamental frequencies 2 : 1 ke ratio mein hain, jaise 220 Hz aur 440 Hz, ek octave door hain, bilkul Activity 10.7 ke Sa aur upar wale Sa ki tarah.

10.7 Sound ka Reflection

Deewar, pahaadi ya jheel ki surface se milne wali sound bas gayab nahi hoti: uska bada hissa wapas uchhal jaata hai. Yeh reflection of sound hai, aur yeh un rules ko follow karta hai jo tumne Grade 8 mein light ke liye seekhe the. Normal (surface ke right angle par line) se measure karein to reflected sound usi angle par nikalti hai jis angle par aane wali sound pahunchi thi. Saath hi, aane ki direction, reflected direction aur normal ek hi plane mein hote hain.

Tum ise do lambi cardboard tubes aur ek hard board se try kar sakte ho: ghadi ki tick ko ek tube mein bhejo aur doosri tube ke end par suno. Tick sabse tez tab hoti hai jab dono tubes normal ke saath barabar angles banaati hain.

10.7.1 Echo

Pahaadon mein ek gehri ghaati ke paar, ya ek bade dam ki deewar ki taraf zor se pukaaro, aur thodi der baad tumhari apni awaaz tumhe jawab deti hai. Jawab deti woh sound ek echo hai.

Asli baat timing ki hai. Agar doosri sound lagbhag second ke dasven hisse (0.1 s) ke andar aaye, to tumhara dimaag do sounds ko ek mein mila deta hai: bahut jaldi do baar taali bajao aur tumhe ek dhundhli taali sunayi degi. Isliye echo tabhi sunayi deta hai jab reflection original ke kam se kam 0.1 s baad lautta hai. Classroom mein deewarein paas hain, reflections usse kahin pehle laut aate hain, aur bas tumhari awaaz mein mil jaate hain. Yeh rule batata hai ki reflect karne wali surface kitni door honi chahiye.

Surface bhi maayne rakhti hai. Khuli chattaan, concrete aur glass zyaadatar sound seedhe wapas bhejte hain, isliye unke echo saaf hote hain. Pedon se dhaki pahaadi sound ko tod kar kai directions mein bikher deti hai. Cushions, carpets aur pardon se bhara kamra iska bada hissa sokh leta hai, isliye koi bhi echo dheema ya dhundhla hota hai.

10.7.2 Reverberation

Khaali school hall mein ek baar taali bajao aur suno: sound ekdum nahi rukti balki ek pal hawa mein tangi rehti hai. Woh deewar se chhat, chhat se farsh aur wapas, baar-baar uchhal rahi hai, aur har uchhaal par thodi energy kho deti hai. Yeh reflections tum tak second ke bas kuch sauven hisse ke gap par (lagbhag 0.05 s se kam) pahunchte hain, isliye alag echoes ke bajaye ek dheemi padti poonchh mein ghul jaate hain. Is der tak tike rehne ko reverberation kehte hain.

Concert halls aur auditoriums design karne wale bilkul sahi maatra chahte hain. Thoda reverberation music ko bhara aur garmahat bhara banata hai; zyada ho to speech gadbad ho jaati hai. Isliye woh stage ke peeche curved reflectors banate hain jo sound ko peeche ki rows tak phenkte hain, aur faltu reflections ko padded seats, carpets, bhaari pardon aur sound sokhne wale panels se kaabu karte hain.

10.8 Ultrasonic aur Infrasonic Waves, aur unke Applications

Jo sounds hum sun nahi sakte, woh bhi sound waves hi hain, aur woh science, medicine aur industry mein powerful tools ban gayi hain.

10.8.1 Echolocation

Wapas bina chaand wali raat ki bat par chalo. Zyaadatar bats sound se shikaar karti hain: udte hue bat ultrasound ke chhote bursts mein awaaz deti hai, lagbhag das har second, jo humare sunne ke liye bahut oonche hain. Har moth, tehni aur deewar ek halka echo wapas phenkti hai. Der bat ko batati hai ki object kitni door hai, aur uske do kaanon ke beech ka farq batata hai ki kis taraf. Moth ke paas aate hue woh aur tezi se awaaz deti hai, lagbhag do sau calls har second tak. Is tarah echoes se cheezein dhoondhne ko echolocation kehte hain. Dolphins aur daant wali whales paani ke andar isi tarah shikaar karti hain, aur oilbirds aur kuch swiftlets ghup andhere caves mein udne ke liye gunjte clicks use karte hain.

Ships paani ke andar yahi idea sonar (sound navigation and ranging) mein use karte hain. Hull ke neeche laga transmitter paani mein ultrasound ki ek pulse bhejta hai, aur ek receiver echo pakadta hai Fig. 10.17. Samudri paani mein sound ek jaani-pehchaani speed se travel karti hai, isliye echo aane tak ka time (10.3) se distance de deta hai. Baar-baar ki pulses submarine, machhliyon ke jhund ya wreck ki direction aur speed bata deti hain.