State the audible range for humans
Scenario
Dogs aisi whistle sun sakte hain jo insaano ko bilkul sunai nahi deti, aur chamgadar (bats) raat ke andhere mein aisi aawazein nikalte hain jo hum nahi sun sakte.
Kya wajah hai ki hamare kaan sab tarah ki aawazein nahi sun paate?
Mental model
Hamare kaan ek radio receiver ki tarah hain jo sirf ek specific range of channels (frequencies) hi pakad sakte hain.
Jaise radio par FM frequency 88 se 108 ke beech milti hai, waise hi human ear sirf unhi sounds ko detect kar sakta hai jinki frequency ek certain minimum (20 Hz) aur maximum (20,000 Hz) limit ke beech hoti hai.
Explanation
Human ear har frequency ki sound nahi sun sakta. Hamari hearing ki ek fix boundary hai, jise **Audible Range** kehte hain. Ek normal insan ke liye ye range **20 Hz se lekar 20,000 Hz (ya 20 kHz)** tak hoti hai. Is range ki sounds ko hi hamara brain process kar pata hai.
Agar koi sound wave 20 Hz se kam frequency ki ho (yaani bahut dheeme vibrate kar rahi ho), toh use hum **Infrasound** (ya infrasonic sound) kehte hain. Hathi (elephants), whales, aur rhinos infrasound mein communicate karte hain. Even earthquakes ke time par pehle infrasound waves produce hoti hain, jinhe kuch janwar sunkar pareshan ho jate hain.
Doosri taraf, agar sound ki frequency 20,000 Hz se zyada ho (yaani bahut fast vibration), toh use **Ultrasound** (ya ultrasonic sound) kehte hain. Dogs, dolphins, aur bats ultrasound ko aasani se sun sakte hain. Bats toh ultrasound ka use karke andhere mein apna rasta dhoondhte hain (echolocation) aur medical field mein bhi ultrasound ka bahut use hota hai (jaise sonography).
Jaise-jaise insaan ki umar badhti hai, uske kaan higher frequencies ke liye kam sensitive ho jate hain, isliye buzurg log (older people) aasaani se high-pitched sounds nahi sun paate.
Worked example
Problem: A vibrating string produces a sound of 15 Hz. Will a normal human being be able to hear it?
- Insaan ka audible range 20 Hz se start hota hai.
- 15 Hz human hearing ki lower limit (20 Hz) se kam hai.
Answer: No, humans cannot hear it because it is an infrasonic sound.
Problem: A bat emits a squeak at a frequency of 50 kHz. Can humans hear this squeak?
- Sabse pehle 50 kHz ko Hz mein convert karenge.
- Ye frequency human audible range (20,000 Hz) se bahut zyada hai.
Answer: No, because it falls in the ultrasonic range, which is above human hearing capacity.
Key points
- Audible Range: The audible range of hearing for average human beings is 20 Hz to 20,000 Hz.
- Infrasound: Sounds with frequencies below 20 Hz. Produced by earthquakes, whales, elephants.
- Ultrasound: Sounds with frequencies above 20,000 Hz. Used by bats, dolphins, dogs, and in medical imaging.
Common mistakes
- Confusing infrasound and ultrasound: 'Infra' ka matlab hai neeche (20 Hz se kam) aur 'ultra' ka matlab hai aage ya upar (20,000 Hz se zyada).
Recall questions
- What is the audible range for humans?
- What do we call sounds with frequencies below 20 Hz?
- What type of sound is produced by an earthquake before the main shock?
Questions & answers
What is the audible range of the average human ear?
The audible range of an average human ear is from 20 Hz to 20,000 Hz.
Approach: Directly state the lower and upper limits of human hearing in Hertz.
Name one animal that uses ultrasound to navigate.
Bats use ultrasound to navigate and find prey.
Approach: Give a common example of an animal using echolocation.