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š” Silence of space
Pump the air out and the ringing bell falls silent — even though you can still see it ringing.
What does the bell jar experiment show?
- An electric bell rings inside a glass bell jar .
- As air is pumped out, the sound gets fainter ; near vacuum, almost no sound is heard.
- Let the air back in and the sound returns — so sound cannot travel through vacuum .
In outer space there is a near vacuum, so sound cannot propagate. That is why astronauts on spacewalks cannot directly hear each other or the clanking of metal — they talk through radios fitted into their spacesuits.
NCERT Question 8 — In a movie, while showing
In a movie, while showing the explosion of a spacecraft in space, a flash of light is shown along with sound at the same time. What are the errors in this depiction?
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āøā¶ Pause and Ponder
3. Assertion (A): We cannot hear a bell ringing in a closed jar after most of the air is pumped out. Reason (R): Sound requires a medium to travel. Answer: (ii) Both A and R are true and R is the correct explanation of A.
Important Definitions
- Vacuum — a space that contains no matter, and therefore no medium for sound to travel through.
- Propagation — the travelling of sound outward from the source through a medium.
