State laws of reflection of sound
Scenario
Agar aap ek deewar par tennis ball fainkte hain, toh ball takra kar wapas aati hai. Theek waise hi sound bhi takra kar wapas aati hai.
Sound deewar se kis direction mein wapas bounce hoti hai?
Mental model
Sound ka bounce hona bilkul light ke bounce hone ya pool table par ball ke bounce hone jaisa hai.
Jis angle par sound wave surface par hit karti hai, theek usi angle par wo wapas bounce hoti hai. Yeh rule sound aur light dono par barabar apply hota hai.
Explanation
Jaise light mirror se reflect hoti hai, waise hi sound bhi solid ya liquid surfaces se takra kar wapas aati hai. Is process ko **Reflection of Sound** kehte hain. Sound ka bounce hona kuch rules follow karta hai, jinhe Laws of Reflection of Sound kehte hain.
First law kehta hai ki sound wave jo surface ko hit karti hai (**incident sound wave**), jo sound wave wapas aati hai (**reflected sound wave**), aur surface par drawn normal (perpendicular line at the point of incidence) — ye teeno ek hi plane (flat surface) mein hote hain.
Second law bahut practical aur useful hai: Angle of incidence ($i$) humesha Angle of reflection ($r$) ke barabar hota hai. Iska matlab hai ki agar ek sound wave deewar se 30 degree ke angle par takrati hai (normal se measured), toh wo 30 degree ke angle par hi wapas bounce hogi.
Inhi laws ki wajah se hum bade halls mein ya mountains ke paas echo sunte hain. Sound badi surfaces jaise pahaad ya buildings se easily reflect ho jati hai, jabki soft surfaces sound ko absorb kar leti hain.
Worked example
Problem: A sound wave hits a smooth solid wall such that the angle it makes with the normal to the wall is 45 degrees. At what angle will the sound reflect from the normal?
- Hamein angle of incidence (normal ke respect mein) diya gaya hai.
- Law of reflection ke according, angle of incidence humesha angle of reflection ke barabar hota hai.
Answer: The sound will reflect at an angle of 45 degrees.
Problem: A student points a hollow tube at a wall to direct a sound wave at a 60-degree angle from the wall's surface. What is the angle of reflection?
- Dhyan dein, ye angle surface ke sath hai, normal ke sath nahi. Normal surface se 90 degree par hota hai.
- Ab law of reflection lagayenge.
Answer: The angle of reflection is 30 degrees.
Key points
- First Law of Reflection: The incident sound wave, the reflected sound wave, and the normal at the point of incidence all lie in the same plane.
- Second Law of Reflection: The angle of incidence is equal to the angle of reflection (angle i = angle r).
Common mistakes
- Measuring the angle from the surface instead of the normal: Angles humesha normal (perpendicular) se measure karne hote hain. Surface se angle measure karna sabse aam galti hoti hai.
Recall questions
- What is the relationship between the angle of incidence and the angle of reflection for sound waves?
- From where do we measure the angle of incidence?
- What is the first law of reflection of sound?
Questions & answers
State two laws of reflection of sound.
1. The angle of incidence is equal to the angle of reflection. 2. The incident sound wave, the reflected sound wave, and the normal at the point of incidence lie in the same plane.
Approach: State exactly as the laws of reflection for light.
Do sound waves obey the same laws of reflection as light waves?
Yes, sound waves follow the same laws of reflection as light.
Approach: Confirm that the laws of reflection apply universally to both sound and light.
Continue learning
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