Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Explain how an echo is produced.
• Calculate the speed of sound using echoes.
• Apply the echo concept to determine the depth of rivers.
• Describe a simple experiment to find the speed of sound.
• Identify career paths related to sound and waves.

Lesson summary

Good day, students. Have you ever shouted in a large, empty hall like the National Theatre or across a valley like the ones near the Kwahu Scarp? You might have heard your own voice come back to you a moment later. That phenomenon is called an echo. It's not just a fun curiosity; it is a fundamental principle of wave physics with powerful real-world applications. In Ghana, this principle is used by our fishing trawlers off the coast of Tema to find fish, by engineers to map the bed of the Volta Lake, and even in our hospitals for medical scans. Today, we will understand the science behind echoes and learn how to use it to perform calculations, such as finding the depth of a river.

Lesson notes

A. The Reflection of Sound and Echoes

First, let's remember that sound is a wave produced by vibrations, which travels through a medium (like air or water). Just like a ball bouncing off a wall, sound waves can also bounce off surfaces. Reflection of Sound: The bouncing back of sound waves when they strike a hard, large surface. Echo: An echo is a reflected sound that is heard distinctly separate from the original sound.

For our brain to distinguish between the original sound and its reflection, there must be a short time delay between them.

Conditions for Hearing a Clear Echo: Time Interval: The time gap between the original sound and the echo must be at least 0.1 seconds. This is because of the "persistence of hearing" of the human ear. Our brain holds onto a sound for about 0.1s, so if the reflected sound arrives sooner than that, it merges with the original sound, and we don't hear a distinct echo. Nature of Reflector: The reflecting surface must be large and hard. A soft surface, like a curtain or thick bush, will absorb most of the sound energy. A hard surface, like a concrete wall, a cliff face, or the seabed, reflects it well. Minimum Distance: There must be a sufficient distance between the source of the sound and the reflector. We can calculate this minimum distance. B. The Mathematics of an Echo

Evaluation guide

• Expla in how an echo comes about and apply the phenomenon in the determination of
• the depth of rivers.
• Think pair share : Using think pair share let s learners employ the concept of relating speed to
• distance and time to establish an equation for the speed of sou nd as far as a reflection of sound.