Introduction
Kya aapne kabhi socha hai ki pahadon mein awaaz gunjti (echo) kyun hai? Ya ambulance ki awaaz paas aate hue tej kyun ho jati hai?
Yeh sab Physics of Sound (Dhwani) ka khel hai.
Agar aap HP TGT Commission (Non-Medical), HP Police, ya SSC CGL ki taiyari kar rahe hain, toh is chapter se 2 sawal pakka aate hain.
Aaj hum padhenge Sound Waves, Speed of Sound, aur Sonar technology ke baare mein.
1. What is Sound? (Dhwani Kya Hai?)
Sound ek prakar ki Energy (Urja) hai jo Vibration (Kamban) se paida hoti hai.
Nature: Sound waves Longitudinal Waves (Anudairdhya Tarang) hoti hain.
Medium: Sound ko chalne ke liye Medium (Solid, Liquid, Gas) ki zaroorat hoti hai.
Exam Fact: Sound Vacuum (Nirvat) mein travel nahi kar sakti. Isliye Chand (Moon) par do log aapas mein baat nahi kar sakte.
2. Frequency Range (Aavriti Range)
Insaan har tarah ki awaaz nahi sun sakta. Frequency ke hisab se sound 3 tarah ki hoti hai:
| Type | Frequency Range | Who can hear it? |
| Infrasonic (Avshravya) | < 20 Hz | Haathi (Elephant), Whale, Earthquake waves. Insaan nahi sun sakta. |
| Audible (Shravya) | 20 Hz - 20,000 Hz | Insaan (Humans) is range mein sunte hain. |
| Ultrasonic (Parashravya) | > 20,000 Hz | Chamgadar (Bat), Kutta (Dog), Dolphin. |
Uses of Ultrasonic Waves:
Sonar: Samundar ki gehrai napne ke liye.
Ultrasound: Pet ki bimari check karne ke liye (Medical).
Cleaning: Ghadi ke purje saaf karne ke liye.
3. Speed of Sound (Dhwani ki Chaal)
Sound ki speed alag-alag cheezon mein alag hoti hai.
Sabse Tej: Solid (Thos) mein (e.g., Steel, Aluminium).
Medium: Liquid (Paani).
Sabse Dheere: Gas (Hawa).
Effect of Temperature:
Tapman (Temperature) badhane par sound ki speed badh jati hai.
Fact: Garmiyon mein awaaz door tak sunayi deti hai kyunki hawa garam hoti hai.
Speed in Air (at 20°C): Approx 343 m/s.
4. Echo (Pratidhwani - Goonj)
Jab hum kisi khali hall ya pahad par chillate hain, toh awaaz wapas aati hai. Ise Echo kehte hain.
Shart (Condition): Echo sunne ke liye source aur deewar ke beech kam se kam 17.2 Meters ki doori honi chahiye.
Agar doori kam hogi, toh dimaag asli awaaz aur echo mein fark nahi kar payega.
5. Sonar & Radar (Difference)
Exam mein aksar confusion hota hai:
SONAR (Sound Navigation And Ranging): Isme Ultrasonic Sound Waves use hoti hain. (Paani ke neeche ships/submarine dhoondhne ke liye).
RADAR (Radio Detection And Ranging): Isme Radio Waves use hoti hain. (Hawa mein hawai jahaz dhoondhne ke liye).
6. Important Phenomena
A. Doppler Effect
Jab koi train horn bajate hue aapki taraf aati hai, toh awaaz Teekhi (High Pitch) lagti hai. Jab door jati hai, toh awaaz Bhaari (Low Pitch) ho jati hai.
Is frequency change ko Doppler Effect kehte hain.
B. Mach Number (Mac Sankhya)
Yeh Jet Planes ki speed napne ke liye use hota hai.
Formula: $\text{Mach Number} = \frac{\text{Speed of Object}}{\text{Speed of Sound}}$
Agar Mach Number 1 se zyada hai, toh use Supersonic kehte hain (e.g., Brahmos Missile).
Agar Mach Number 5 se zyada hai, toh use Hypersonic kehte hain.
C. Sonic Boom
Jab koi plane sound ki speed se tej chalta hai, toh wo ek tez dhamaka (Shockwave) paida karta hai, jise Sonic Boom kehte hain. Isse khidki ke sheeshe toot sakte hain.
7. Question Bank (Exam Wale Sawal)
Q1. Sound sabse tej kisme chalti hai?
(A) Hawa
(B) Paani
(C) Steel ✅
(D) Vacuum
Q2. Chand par bomb phatne ki awaaz dharti par kitni der mein aayegi?
(A) 10 min
(B) 20 min
(C) Kabhi nahi sunayi degi ✅ (Kyunki beech mein Vacuum hai).
Q3. Chamgadar (Bat) raat mein kaise udte hain?
Ans: Wo Ultrasonic Waves chodte hain jo shikaar se takra kar wapas aati hain.
8. Characteristics of Sound (Dhwani ke Gun)
Sound waves ko pehchanne ke liye 3 mukhya cheezein hoti hain. Exam mein yahan se confusion wale sawal aate hain.
A. Loudness (Prabalta/Tezi)
Yeh batata hai ki awaaz kitni tez ya dheemi hai.
Dependence: Loudness Amplitude (Aayam) par depend karti hai.
Agar Amplitude zyada hoga, toh awaaz Tez (Loud) hogi (Jaise Sher ki dahad).
Agar Amplitude kam hoga, toh awaaz Dheemi (Soft) hogi (Jaise machhar ki bhin-bhinahat).
Unit: Iski unit Decibel (dB) hai.
Normal Baat-cheet: 60 dB.
Noise (Shor): 80 dB se upar.
B. Pitch (Taaratva/Teekhapan)
Yeh batata hai ki awaaz kitni "Baareek" ya "Moti" hai.
Dependence: Pitch Frequency (Aavriti) par depend karti hai.
High Pitch: Auraton (Females) aur bacchon ki awaaz ki frequency zyada hoti hai, isliye wo Teekhi hoti hai.
Low Pitch: Mardon (Males) ki awaaz ki frequency kam hoti hai, isliye wo Bhaari hoti hai.
C. Quality or Timbre (Gunata)
Agar do logon ki Loudness aur Pitch same ho, tab bhi hum unki awaaz pehchan lete hain. Yeh Quality ke karan hota hai. Isse hum Guitar aur Piano ki awaaz mein fark karte hain.
9. Factors Affecting Speed of Sound (Dhwani ki Chaal par Prabhav)
SSC aur HP Police mein yahan se "True/False" sawal aate hain.
Effect of Density (Ghanatva):
Formula: $v \propto \frac{1}{\sqrt{\rho}}$
Agar gas bhari (dense) hogi, toh sound ki speed kam hogi.
Agar gas halki hogi (Hydrogen), toh sound tej chalegi.
Effect of Humidity (Nami):
Barsaat ke mausam mein hawa mein Nami (Humidity) badh jati hai.
Nami wali hawa, sukhi hawa se halki (low density) hoti hai.
Result: Barsaat mein sound ki speed Badh jati hai. Isliye train ki siti barsaat mein door tak sunayi deti hai.
Effect of Pressure (Daab):
Most Important: Agar temperature same rahe, toh Pressure badhane ya ghatane se Sound ki speed par KOI ASAR NAHI padta.
10. Resonance (Anunaad) - The Bridge Breaker
Kabhi socha hai ki fauj (army) ko pul (bridge) par "Kadamtaal" (March Past) karne se kyun roka jata hai?
Reason: Jab fauji ek saath pair patakte hain, toh ek frequency paida hoti hai.
Agar yeh frequency pul ki "Natural Frequency" se match kar jaye, toh pul bahut zor se hilne lagta hai aur Toot sakta hai. Is ghatna ko Resonance kehte hain.
Example: 1940 mein America ka Tacoma Narrows Bridge hawa ki wajah se resonance hone par toot gaya tha.
11. Reflection of Sound (Laws)
Jaise light reflect hoti hai, waise sound bhi hoti hai.
Iska use hum daily life mein dekhte hain:
Megaphone / Loudspeaker: Yeh sound ko reflect karke ek hi disha (direction) mein bhejta hai taaki awaaz door tak jaye.
Stethoscope: Doctor ka stethoscope sound ki Multiple Reflection par kaam karta hai, jisse dil ki dhadkan kaan tak pahunchti hai.
Cinema Hall: Hall ki chhatein (ceilings) curved banayi jati hain taaki sound reflect hokar har kone mein baithe darshak tak pahunche.
12. Human Ear (Kaan kaise sunta hai?)
Thoda Biology bhi zaroori hai. Kaan ke 3 hisse hote hain:
Outer Ear (Pinna): Yeh awaaz ko ikhatta karta hai.
Middle Ear: Yahan ek Eardrum (Kaan ka parda) hota hai. Iske saath 3 haddiyan hoti hain: Malleus, Incus, Stapes.
Fact: Stapes manav sharir ki sabse chhoti haddi hai.
Inner Ear (Cochlea): Yeh vibrations ko electric signal mein badal kar dimaag (Brain) tak bhejta hai.
Conclusion
Sound chapter chhota hai par scoring hai. Doppler Effect aur Ultrasonic uses ko ache se yaad kar lein.
Next article mein hum Light (Prakash) aur Human Eye ke baare mein padhenge.
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