Lesson Notes By Weeks and Term v4 - SHS 1
WAVES
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WAVES
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Subject: Physics
Class: SHS 1
Term: 2nd Term
Week: 1
Grade code: 1.2.2.LI.1
Strand code: 2
Sub-strand code: 2
Content standard code: 1.2.2.CS.2
Indicator code: 1.2.2.LI.1
Theme: ENERGY
Subtheme: WAVES
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This lesson introduces the fascinating phenomenon of refraction, which is the bending of waves. We encounter refraction every day without even thinking about it. When a fisherman tries to spear a fish in the river, when we see a spoon looking "broken" in a glass of water, or even when we wear spectacles to see clearly, we are experiencing the effects of refraction. Understanding this concept is fundamental to optics and explains how lenses, prisms, and our own eyes work. By exploring why waves bend when they move from one substance to another, we unlock the principles behind many important technologies.
Activity 1: The "Bent" Pencil (Engage) *(This activity corresponds to the NaCCA exemplar)* Procedure: Fill a transparent bowl or glass about two-thirds full with water. Place a pencil or a straight stick obliquely (at an angle) into the water. Observation: Ask learners to look at the pencil from the side and from above. They will observe that the pencil appears bent or broken at the point where it enters the water. Question: "Why do you think the straight pencil looks bent?" Explanation: This is not a magic trick! It is a direct result of refraction. The light rays coming from the part of the pencil in the water travel through the water and then into the air before reaching our eyes. As the light crosses the boundary between water and air, it changes direction, or *bends*. Our brain assumes light travels in a straight line, so it traces the rays back to a "virtual" position, making the pencil appear bent. What is Refraction?
Refraction is the bending of a wave as it passes from one medium to another. A medium is any substance that a wave can travel through (e.g., air, water, glass, diamond).
Why does refraction happen?
The single most important reason for refraction is a change in the speed of the wave. When light travels from a *less dense* medium (like air) to a *denser* medium (like water or glass), it slows down. This causes it to bend towards the normal. When light travels from a *denser* medium (like water) to a *less dense* medium (like air), it speeds up. This causes it to bend away from the normal.