Physicsmedium · Past Paper
What is the minimum distance required between a source and a reflector to hear a distinct echo in air at 20 degrees Celsius?
A1.7 meters
B17.2 meters
C34.4 meters
D172 meters
✓ Correct Answer: B — 17.2 meters
To hear an echo, the sound must travel to the reflector and back in at least 0.1 seconds, which requires a minimum distance of about 17.2 meters at standard speed.
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