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Speed of Sound and Echoes
Echo = reflected sound; distance = vt/2.
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Speed of Sound and Echoes
Recommended for Class 10
Speed of Sound and Echoes
The speed of sound is the distance travelled by a sound wave per unit time.
Sound speed depends on the medium.
It is generally:
fastest in solids,
slower in liquids,
slowest in gases.
In air near room temperature, a commonly used approximate value is:
**v ≈ 340 m/s**
Why Medium Matters
Sound moves through interactions between neighbouring particles.
Materials in which disturbances are transferred efficiently can transmit sound more rapidly.
Echo
An echo is a reflected sound heard separately from the original sound.
The sound travels to a reflecting surface and then returns to the listener.
Echo Distance Formula
Because the sound travels to the obstacle and back:
**distance to obstacle = vt/2**
where:
v = sound speed;
t = total round-trip time.
Worked Example
Echo time = 2.0 s.
v = 340 m/s.
Distance:
**d = vt/2**
= 340 × 22
= **340 m**
Speed of Sound and Echoes — Advanced
Common Mistakes
Common Mistakes
- Mistake
Do not forget division by 2 in echo-distance calculations.
- Mistake
Echo time is round-trip time.
- Mistake
Sound speed is not the same in every medium.
Revision Zone
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Practice
PQ
Q1. Define sound speed.
PQ
Q2. Define echo.
PQ
Q3. Why divide echo time by two?
PQ
Q4. Calculate distance for t=0.5 s, v=340 m/s.
PQ
Q5. Compare sound speed in solids and gases.
Exam Practice
EQ
Q1. Define echo.
EQ
Q2. Derive d=vt/2.
EQ
Q3. Calculate an echo distance.
EQ
Q4. Explain why sound speed differs between media.
EQ
Q5. State approximate speed in air.
School-standard facts for Matric and Intermediate. Original explanations — not copied from textbooks.