CBSE Science Class 8 Sound Notes Chapter 10 - FREE PDF Download
FAQs on Sound Class 8 Notes: CBSE Science Chapter 10
1. What is the basic principle of sound production and propagation?
Sound is produced by vibrating objects. These vibrations create disturbances in the surrounding medium (like air, water, or solids), causing particles to vibrate and pass the energy along. This transfer of energy through a medium is how sound propagates. Sound cannot travel in a vacuum because there are no particles to carry the vibrations.
2. What are the main characteristics used to describe a sound wave for revision?
For a quick revision, the main characteristics of a sound wave are:
- Amplitude: The maximum displacement of a vibrating particle from its mean position. It determines the loudness of the sound.
- Frequency: The number of oscillations per second, measured in Hertz (Hz). It determines the pitch of the sound.
- Time Period: The time taken to complete one full oscillation. It is the inverse of frequency.
3. How can you summarise the difference between loudness and pitch?
Loudness and pitch are two distinct properties of sound. Loudness is determined by the amplitude of the sound wave; a larger amplitude results in a louder sound. It is measured in decibels (dB). Pitch, on the other hand, is determined by the frequency of the wave; a higher frequency results in a higher-pitched (or more shrill) sound.
4. What is the audible range for humans, and how are sounds outside this range classified?
The range of frequencies a human ear can detect is known as the audible range, which is typically from 20 Hz to 20,000 Hz (20 kHz). Sounds outside this range are classified as:
- Infrasound: Sounds with frequencies below 20 Hz.
- Ultrasound: Sounds with frequencies above 20,000 Hz.
5. What is the key difference between music and noise?
The key difference for revision lies in the nature of the vibrations. Music consists of pleasant, organised sounds produced by regular, periodic vibrations, creating a clear rhythm and melody. In contrast, Noise is an unpleasant or jarring sound produced by irregular, non-periodic vibrations, and it lacks a discernible pattern.
6. How does the human ear work to perceive sound?
The ear converts sound waves into electrical signals for the brain. Sound waves enter the outer ear and travel to the eardrum, causing it to vibrate. These vibrations are amplified by three tiny bones in the middle ear and passed to the cochlea in the inner ear. The cochlea transforms these vibrations into electrical signals, which the auditory nerve sends to the brain for interpretation.
7. What is noise pollution and what are some measures to limit it?
Noise pollution is the presence of excessive, unwanted, or disruptive sound that has harmful effects on human health and the environment. Key measures to limit it include planting trees as sound barriers, using soundproofing materials in buildings, enforcing restrictions on loudspeakers, and designing quieter machinery and vehicle engines.
8. Why can you hear an approaching train through the rail track before you hear it through the air?
This happens because sound travels at different speeds through different media. Sound propagates much faster through solids, like the steel of a rail track, than it does through gases, like air. The particles in a solid are packed much more tightly, allowing vibrations to be transferred more efficiently and quickly from one particle to the next.
9. How do the concepts of amplitude and frequency relate to what we actually hear every day?
These physical properties directly correspond to our perception of sound. The amplitude of a sound wave determines its loudness or volume; a high-amplitude wave is perceived as a loud sound, while a low-amplitude wave is a quiet sound. The frequency of the wave determines its pitch; a high-frequency wave is heard as a high-pitched or shrill sound, like a whistle.
10. Why do a guitar and a piano sound different even when playing the same note at the same volume?
This is due to a characteristic called quality or timbre. While the note may have the same fundamental frequency (pitch) and amplitude (loudness), each instrument produces a unique mix of additional frequencies called overtones. The specific combination and intensity of these overtones give each instrument its distinct sound, allowing our ears to distinguish between them.
11. If a tree falls in a forest with no one to hear it, does it make a sound?
From a physics standpoint, the falling tree definitely creates sound waves. The impact causes vibrations that propagate through the air. However, the term "sound" also refers to the perception of these waves. Without an ear and a brain to receive and interpret these vibrations, the sensation of sound does not occur. So, while the physical phenomenon exists, the perceptual experience does not.
