Lesson Notes By Weeks and Term v4 - SHS 2
WAVES
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WAVES
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Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 18
Grade code: 2.2.2.LI.3
Strand code: 2
Sub-strand code: 2
Content standard code: 2.2.2.CS.2
Indicator code: 2.2.2.LI.3
Theme: ENERGY
Subtheme: WAVES
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Welcome, learners! Have you ever shouted in a large, empty room like the National Theatre hall, or across a valley near Aburi, and heard your own voice come back to you a moment later? That repeating sound is called an echo. This is a common experience, but it is also a powerful physics principle at work. An echo is simply a reflection of sound waves. In this lesson, we will explore exactly how echoes are formed. More importantly, we will learn how this simple phenomenon is used in advanced technology to solve real-world problems, such as measuring the depth of the Volta Lake, helping fishermen in Tema find fish, and even allowing doctors at Korle Bu to see inside the human body.
Part 1: The Science of an Echo
A. What is an Echo? An echo is a reflection of sound that arrives at the listener with a delay after the direct sound.
For you to hear a distinct echo, two main conditions must be met: There must be a large, hard, and smooth surface to reflect the sound. A concrete wall, a cliff face, or a large building are good reflectors. Soft surfaces like curtains or grass absorb sound and do not produce good echoes. The time delay between the original sound and the reflected sound must be long enough for our brain to distinguish them. The human ear can distinguish two separate sounds if they are at least 0.1 seconds apart. This is called the persistence of hearing.
B. The Journey of an Echo Imagine you are standing some distance away from a tall wall and you clap your hands. The sound from your clap travels from your hands through the air to the wall. The sound wave hits the wall and bounces off it (this is reflection). The reflected sound wave then travels back from the wall to your ears.