Describe an echo as the reflection of sound waves

3.4 Sound – Echoes

What is an Echo?

An echo is a reflection of sound waves that returns to the listener after bouncing off a surface. Think of shouting in a canyon: the sound travels out, hits the distant walls, and comes back to you, just like a mirror for sound.

How Echoes Form

1️⃣ Emission: You produce a sound wave (e.g., a shout). 2️⃣ Propagation: The wave travels through air at speed $v \approx 340\,\text{m/s}$ at room temperature. 3️⃣ Reflection: When the wave reaches a hard surface (rock, wall, mountain), it bounces back. 4️⃣ Reception: The reflected wave travels back to you and is heard as an echo.

• Echoes require a clear, hard surface far enough away.
• The time delay between the original sound and the echo depends on the distance $d$ to the reflecting surface: $$t = \frac{2d}{v}$$
• Because sound loses energy when it travels, echoes are usually fainter than the original sound.

Echo vs. Direct Sound