Laws of Reflection of Sound (Verification) MCQs Quiz | Class 9
This Class IX Science (Code 086) quiz focuses on the Practicals (Unit III) topic: Laws of Reflection of Sound. It covers the incident and reflected sound concepts, experimental conditions, and conclusion statements. Attempt the 10 questions below to verify your understanding, check your score, and download the solution PDF.
Overview: Laws of Reflection of Sound
Just like light, sound gets reflected when it strikes a hard surface. The bouncing back of sound waves from a surface is called reflection of sound. For the Class 9 practical verification, we observe two main laws that govern this phenomenon.
The Two Laws of Reflection
- First Law: The angle of incidence of sound is always equal to the angle of reflection of sound. (Angle i = Angle r).
- Second Law: The incident sound wave, the reflected sound wave, and the normal to the reflecting surface at the point of incidence all lie in the same plane.
Experimental Verification
To verify these laws, two long identical hollow pipes are used. They are arranged at an angle on a table near a wall or a rigid obstacle (the reflector). A source of sound (like a ticking clock or mobile phone) is placed at the end of one pipe. The ear is placed at the end of the second pipe. The position of the second pipe is adjusted until the sound heard is loudest.
| Component | Requirement | Reason |
|---|---|---|
| Reflecting Surface | Hard and Smooth (e.g., Wall, Metal Plate) | Reflects sound efficiently without absorption. |
| Pipes/Tubes | Hollow, smooth interior | Guides sound waves towards and away from the wall. |
| Background | Quiet | To hear the reflected sound clearly. |
Key Conclusions
- Sound follows the same laws of reflection as light.
- Soft, porous materials (like curtains, foam, or carpet) are bad reflectors because they absorb sound.
- Hard surfaces (like brick walls, wood, metals) are good reflectors.
Extra Practice Questions
- Q: Why are curved ceilings used in concert halls? A: To reflect sound uniformly to all parts of the hall.
- Q: What is the normal? A: An imaginary line perpendicular to the reflecting surface at the point of incidence.
- Q: Does frequency change upon reflection? A: No, frequency remains the same.
- Q: What is an echo? A: A distinct sound heard after reflection from a distant obstacle.
- Q: Which material is used for soundproofing? A: Porous materials like thermocol or heavy curtains to absorb sound.
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