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: 1st Term
Week: 13
Grade code: 1.2.2.LI.2
Strand code: 2
Sub-strand code: 2
Content standard code: 1.2.2.CS.1
Indicator code: 1.2.2.LI.2
Theme: ENERGY
Subtheme: WAVES
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This lesson explores the fascinating phenomenon of reflection, which is a fundamental behaviour of waves, especially light. Reflection is all around us in Ghana. We see it every morning when we look in a mirror to get ready for school, when we see the beautiful sunset reflected on the surface of the Volta Lake, or even when a driver uses a rear-view mirror to navigate the busy streets of Accra. Understanding how reflection works is the first step to understanding more complex optical instruments like telescopes, cameras, and periscopes. This lesson will move from simple observation to a scientific deduction of the laws that govern this everyday experience.
2.1 What is Reflection?
Reflection is the bouncing back of a wave (like light, sound, or water waves) when it hits a boundary or surface that it cannot pass through. In this lesson, we will focus on the reflection of light from a smooth, polished surface like a plane mirror. 2.2 Key Terms and Definitions
To understand the laws of reflection, we must first understand the language used to describe it. Consider a ray of light hitting a plane mirror.
(Teacher's Note: Draw this diagram on the board and label it as you explain each term. This is the most important visual for the lesson.) Plane Mirror: A mirror with a flat reflective surface. Incident Ray: The ray of light that travels from a light source and strikes the surface of the mirror. (In the diagram, this is the ray PO). Reflected Ray: The ray of light that bounces off the surface of the mirror. (In the diagram, this is the ray OQ). Point of Incidence: The exact point on the mirror where the incident ray strikes it. (Point O). Normal (N): An imaginary straight line drawn at the point of incidence, perpendicular (at 90°) to the surface of the mirror. This line is crucial for measuring our angles. Angle of Incidence (i): The angle between the incident ray and the normal. (Important: It is NOT the angle between the ray and the mirror surface). Angle of Reflection (r): The angle between the reflected ray and the normal. 2.3 Deducing the Laws of Reflection: An Experiment