Reflection of Sound MCQs Quiz | Class 9
This quiz covers Unit III: Motion, Force and Work for Class IX Science (Code 086). It focuses on the Topic: Reflection of Sound, including basic laws of reflection and everyday examples like echoes, reverberation, and applications like stethoscopes. Complete the 10 MCQs below to test your understanding, view your score, and download a PDF answer sheet.
Overview of Reflection of Sound
Sound waves, like light waves, bounce off surfaces when they hit an obstacle. This phenomenon is called the reflection of sound. It follows specific laws and is responsible for many acoustic phenomena we experience daily, such as echoes and reverberations.
Laws of Reflection of Sound
The reflection of sound obeys the same laws as the reflection of light:
- First Law: The angle of incidence is always equal to the angle of reflection.
- Second Law: The incident sound wave, the reflected sound wave, and the normal at the point of incidence all lie in the same plane.
Common Phenomena
| Phenomenon | Description | Condition |
|---|---|---|
| Echo | A distinct repetition of the original sound. | Time gap between original and reflected sound must be at least 0.1 seconds. Minimum distance is approx 17.2 meters. |
| Reverberation | The persistence of sound in a hall due to repeated reflections. | Occurs in closed spaces where sound reflects multiple times before fading out. |
Applications of Multiple Reflection
- Megaphones and Horns: Designed to send sound in a particular direction without spreading it in all directions. A tube followed by a conical opening reflects sound successively to guide it forward.
- Stethoscope: A medical instrument used for listening to sounds produced within the body. The sound of the patient’s heartbeat reaches the doctor’s ears by multiple reflection of sound.
- Curved Ceilings: Concert halls and cinema halls have curved ceilings so that sound reaches all corners of the hall after reflection.
- Sound Boards: Curved sound boards are placed behind the stage so that sound, after reflecting from the sound board, spreads evenly across the width of the hall.
Key Facts for Revision
- To hear a distinct echo, the obstacle must be rigid and large.
- Soft materials like curtains, carpets, and fibreboard are used in auditoriums to absorb sound and reduce excessive reverberation.
- The sensation of sound persists in our brain for about 0.1 seconds.
- Sound navigation systems like SONAR use the reflection of ultrasonic waves to detect underwater objects.
Extra Practice Questions
1. Why are the ceilings of concert halls curved?
Answer: To ensure sound is reflected evenly to all parts of the audience.
2. What is the minimum time interval required between the original sound and the reflected sound to hear an echo?
Answer: 0.1 seconds.
3. Name the device used by doctors to listen to heartbeats.
Answer: Stethoscope.
4. Which property of sound is responsible for reverberation?
Answer: Multiple reflection of sound.
5. If the temperature of air increases, how does the minimum distance for an echo change?
Answer: Since the speed of sound increases with temperature, the minimum distance required (Speed x Time / 2) also increases.
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