Summary & Quick Quiz ശബ്ദം
The whole chapter on one page: the nine key boxes of the textbook, every fact and formula you need, the mistakes to avoid, flashcards, a scored quiz and your study checklist.
1. The chapter in one picture
Read it clockwise from the top left: a source vibrates; the vibrations travel through a medium (never through vacuum) at a speed that depends on the medium; the compressions and rarefactions make our eardrum vibrate and the brain perceives sound; regular vibrations give music, irregular ones noise; too much unwanted sound is noise pollution.
2. The key boxes of the textbook
Sound is a form of energy that produces the sensation of hearing. – page 5
Sound is produced by the vibration of objects. Objects that produce sound are sources of sound. – page 5
Every source of sound has a main part that vibrates. The sound we hear is the combined effect of the vibrations of several parts and of the surrounding air. In musical instruments, the main part and the associated parts together make the sound sweeter and louder. – page 5
Sound reaches our ears by travelling through air. Sound cannot travel through vacuum. – page 6
Sound can travel through gases, liquids and solids. Sound needs a medium to travel. – page 6
The speed of sound is different in different media, and it increases when the temperature of the medium increases. – page 7
A vibrating object makes rapid pressure variations in the air; they travel through the medium and make the eardrum vibrate; the vibrations reach the inner ear and signals go to the brain. We need a source, a medium and an organ of hearing. – page 8
Music: sound from regular vibrations, pleasant to hear. Noise: sound from irregular vibrations, unpleasant. – page 9
Unnecessary sound that is unbearable and uncomfortable and that harms humans and other living things is noise pollution. – page 9
3. Facts & formulas
📐 Facts & formulas card
light: 3 × 108 m/s · sound in air ≈ 350 m/s (347 m/s at 25 °C)
thunder: distance ≈ 350 × seconds (about 3 s per km)
| Idea | Remember |
|---|---|
| Source of sound | anything that vibrates: tuning fork, bell, strings, stretched skin, air column, vocal cords, the wings of a bee or a mosquito |
| Main vs associated parts | veena / violin: strings | body, air inside · chenda / tabla / mridangam: stretched skin | body, air inside · elathalam: metal plates | air · harmonium: reeds | air column, wooden box · odakkuzhal, bugle: air column |
| Our voice | vocal cords in the larynx (voice box) vibrate; the air in the throat, mouth and nose and the muscles vibrate with them |
| Medium | solid, liquid or gas – never vacuum (bell jar, astronauts, the Moon); snakes feel ground vibrations, whales and dolphins call through water |
| How sound travels | compressions (C, high pressure) and rarefactions (R, low pressure); the particles only vibrate to and fro – they do not travel with the sound |
| To hear a sound | source + medium + organ of hearing; outer ear (pinna) → ear canal → eardrum → inner ear → brain |
| Hearing loss | found with an audiometer; a hearing aid helps; World Hearing Day is 3 March; treat people with hearing loss with kindness and include them |
| Ear care | never put pins, sticks or cotton buds deep into the ear; avoid loud sound and loud headphones; see a doctor for pain or discharge |
| Music vs noise | regular vs irregular vibrations; music becomes noise when it is too loud |
| Reduce noise pollution | no air horns, working silencers, box-type speakers, no loudspeakers 10 pm – 6 am, trees, silence near hospitals, schools and courts, ear plugs and ear muffs |
| State | Medium മാധ്യമം | Speed of sound at 25 °C (m/s) – Table 8.3 |
|---|---|---|
| Solid ഖരം | aluminium അലുമിനിയം | 6423 |
| steel സ്റ്റീൽ | 5944 | |
| Liquid ദ്രാവകം | sea water കടൽജലം | 1525 |
| pure water ശുദ്ധജലം | 1485 | |
| Gas വാതകം | helium ഹീലിയം | 968 |
| air വായു | 347 |
Go further beyond the textbook
| Idea | Remember |
|---|---|
| Temperature | in air the speed rises by about 0.6 m/s for every 1 °C |
| Echo, SONAR | depth = speed × time ÷ 2 (the sound goes there and back); sea water 1525 m/s |
| Pitch and loudness | more vibrations per second (frequency, in hertz) → higher pitch; bigger vibrations (amplitude) → louder; humans hear about 20 Hz – 20 000 Hz; above that is ultrasound |
| Decibels (approx.) | normal talk ≈ 60 dB · busy traffic ≈ 80–90 dB · firecracker ≥ 120 dB · harmful above ≈ 85 dB for long exposure |
- Saying sound can travel through vacuum or in space. It cannot – that is why astronauts use radio.
- Thinking the air particles travel from the source to the ear. They only vibrate to and fro about their places; the disturbance (the compressions and rarefactions) travels.
- Saying sound is fastest in gases. It is slowest in gases and fastest in solids (air 347 m/s, aluminium 6423 m/s).
- Saying the speed of sound decreases with temperature. It increases.
- Forgetting that light reaches us almost instantly. In thunder and firecracker sums the whole delay is the time taken by the sound.
- Naming only the main vibrating part and forgetting the associated parts (or the other way round) in Table 8.1 questions.
- Writing “noise” for every loud sound and “music” for every soft sound. The difference is regular vs irregular vibration – and loud music can become noise.
- Putting objects into the ear to clean it. Pins, sticks and deep cotton buds can tear the eardrum; wounds there heal slowly and get infected.
4. Flashcards
Click a card to flip it.
5. Scored quiz
Answer all sixteen, then press Check my answers. Each wrong answer shows the page to revise. For number answers type only the number.
6. Your study checklist
Ticks come from “Mark this page as completed” at the bottom of each page.
Next: the model test paper ▶ – attempt it on paper with a timer first, then check with the solved paper.