Sound
Overview
The beat of a tabla, a mother's voice, the noise of a city — all of these are sound. How sound is produced, how we hear it, the difference between loudness and pitch, and noise pollution — all of this is covered in this chapter.
Typed Notes
Sound is produced by vibration
The source of every sound is vibration: the membrane of a tabla, the string of a guitar, your vocal cords (which vibrate when you speak). Place your hand on your throat and speak — you will feel the vibration. When the vibration stops, the sound stops too (hold a guitar string after plucking it — the sound disappears). This vibration travels forward through air (or water or metal) — like a wave — and reaches our ears.
A medium is necessary — sound cannot travel through vacuum
Sound needs a medium to travel — particles that push the vibration forward: solid (fastest speed — put your ear on a railway track), liquid (sound travels through water too), gas (air — how our voices travel). In a vacuum (without air) — sound cannot travel: in the bell jar experiment, when air is pumped out of the jar containing a ringing bell, you can see the bell but cannot hear it. This is why, in space (which is a vacuum), you cannot hear even a scream.
Loudness vs Pitch
(1) Loudness — how strong the sound is: it depends on the size of vibration (amplitude) — if you hit a drum hard, the vibration is large and the sound is loud; unit is decibel (dB): whisper is 30 dB, normal conversation is 60 dB, a rock concert is 110 dB (harmful above 85 dB). (2) Pitch — whether the sound is thin or thick: it depends on the speed of vibration (frequency) — a mosquito vibrates fast, producing a thin/shrill sound; a lion vibrates slowly, producing a thick/heavy sound. Girls and boys have different pitches, and so does a siren. High pitch sounds — like a baby's cry — can be heard from far away. The two properties are independent: a sound can be loud and thick (drum), or soft and thin (some notes on a flute).
The ear, music vs noise, and pollution
Ear: the pinna (outer ear — collects sound waves) → ear canal (the passage) → eardrum (a thin membrane — vibrates) → 3 tiny bones (hammer, anvil, stirrup — they amplify the vibration) → cochlea (snail-shaped structure — hair cells convert vibration into nerve signals) → brain. Keep your ear clean and safe — never insert a pin or sharp object inside! Music — pleasant (has rhythm and tune); noise — unpleasant (random and irregular). Noise pollution: traffic horns, factories, loudspeakers, DJ systems — effects include: hearing loss, stress, disturbed sleep, and high blood pressure. Remedies: fit silencers, reduce honking (no-horn zones near hospitals), locate factories away from cities, plant trees (they absorb sound), and use earplugs (for factory workers).
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Sound is produced by vibration — when something moves back and forth (a string, a membrane, air) — it creates sound.
- 02A medium is required: solid > liquid > gas (order of speed); sound cannot travel through vacuum — proven by the bell in a jar experiment.
- 03Loudness — the size of vibration (amplitude): larger amplitude = louder sound; unit is decibel (dB). Pitch — the speed of vibration (frequency): faster vibration = thin/shrill sound (mosquito), slower vibration = thick/heavy sound (lion).
- 04Human ear: pinna (outer part) → ear canal → eardrum (thin membrane — vibrates) → 3 small bones (amplify the sound) → cochlea (sends nerve signal) → brain.
- 05Music (pleasant to the mind) vs noise (unpleasant); Noise pollution: traffic, factories, loudspeakers — causes hearing loss and stress; remedies include silencers, less honking, factories away from cities, and earplugs.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
How is sound produced? Give one example.
Why cannot sound travel through vacuum?
What is the difference between loudness and pitch?
How can you hear a distant train by placing your ear on a railway track?
Write the 4 main parts of the human ear in the correct sequence.
Write 2 sources and 2 remedies of noise pollution.
Sound = vibration; a medium is necessary (solid > liquid > gas; not in vacuum — bell jar experiment). Loudness = amplitude (dB), pitch = frequency (shrill or thick). Ear: pinna → eardrum → 3 bones → cochlea → brain. Music vs noise; noise pollution (traffic, loudspeakers) — causes hearing loss and stress — remedies: silencers, less honking, planting trees.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.What produces sound?
Q2.What happens to sound in a vacuum?
Q3.Which is an example of a thin (shrill) sound?
Q4.What is a way to protect yourself from noise pollution?
Mark karo — dashboard par progress dikhega.