Question

what is an echo?
multiple choice
a reflected sound you hear after 0.1 s of the original.
a reflected sound you hear within 0.1 s of the original.
it is a refracted sound wave.
it is any reflected sound wave that becomes broken into two parts.

Explanation:

An echo is a reflected sound. For a sound to be perceived as an echo, the time - delay between the original sound and the reflected sound should be at least \(0.1\) s. If the reflected sound is heard within \(0.1\) s of the original, it is called a reverberation (not an echo). Also, an echo is a reflected sound, not a refracted sound wave. And the description of "any reflected sound wave that becomes broken into two parts" is incorrect.

Answer:

A. A reflected sound you hear after \(0.1\) s of the original.