Explain echoes as reflected sound
Trace an outward and reflected return path and distinguish an echo from a fresh source sound.
Core and Extended; Physics 0625, 2026–2028. Follow the selected spectrum or sound section. Diagrams illustrate stated ideal models and supplied data. Written practice is self-checked.
Before you begin
- Describe sound propagation in a medium.
- Distinguish a direct path from a reflected path.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What physical effect can return a sound pulse from a wall?
What you will learn
- Describe an echo as reflection of sound.
- Explain why the returned disturbance arrives later than the direct sound.
Trace the reflected path
An echo is reflected sound. A pulse travels through a medium, reaches a reflecting surface and returns toward a receiver. A large suitably placed hard surface can reflect enough sound for a distinct returned pulse to be detected; some energy can also be absorbed or scattered.
For a source and receiver at approximately the same position, the reflected route travels to the surface and back. The return arrives later because this route is longer than the local direct path. A reflected pulse is not a new independent source repeating the original message.
Distinguish an echo from other received signals
Separate echoes require the returned sound to be distinguishable from the original and other reflections. Closely spaced reflections may overlap as reverberation instead of a clearly separated echo. Do not count every recorded peak as an independent reflected journey without identifying it.
Moving the reflecting surface farther away increases the return delay at the same medium speed. A weaker return can reflect absorption, spreading or the geometry; it does not by itself prove a different wave speed. Reception needs a complete material path, just as direct sound does.
Pause and explain
Why does a farther wall give a later echo at the same sound speed?
Worked example
A sound pulse reaches a wall and a later pulse returns to a nearby source receiver. Explain the later pulse.
Show the worked solution
- The original sound travels to the wall.
- Some sound is reflected back.
- The longer outward-and-return route gives the later arrival.
Answer An echo: reflected sound arriving after a longer path.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Define an echo and name its producing effect.
Give me a hint
Use the original disturbance and its return.
Compare my reasoning
- Sound travels to a boundary.
- The boundary reflects some of it.
- The returned sound is an echo.
An echo is reflected sound.
Look for these in your work
- State reflection.
- Identify a returned disturbance.
Describe the two legs for a collocated source and receiver facing a reflecting wall.
Give me a hint
Trace the pulse before and after reflection.
Compare my reasoning
- The outward leg runs from source to wall.
- Reflection changes the travel direction.
- The return leg runs from wall to receiver.
Source → wall → receiver; an outward and a return leg.
Look for these in your work
- Include both legs.
- Keep the receiver position explicit.
A recorded later pulse is much weaker. Does this prove sound slowed down?
Give me a hint
Separate strength from measured path and timing.
Compare my reasoning
- Spreading or absorption can weaken the return.
- Speed requires distance and time information.
- Amplitude loss alone does not establish reduced speed.
No; a weaker echo does not by itself measure a slower wave.
Look for these in your work
- Name a strength-loss cause.
- State the missing speed evidence.
Common mistakes
- The return is reflected sound, not necessarily a new source.
- An echo route contains outward and return legs.
- Amplitude alone does not measure propagation speed.
What can you explain now?
What is an echo?
Compare with the explanation
Reflected sound.
A reflecting surface returns part of a sound disturbance toward a receiver.
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Make it stick
Explain an echo, trace its complete path and distinguish delay evidence from amplitude evidence.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.