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: 3
Grade code: 1.2.2.LI.4
Strand code: 2
Sub-strand code: 2
Content standard code: 1.2.2.CS.2
Indicator code: 1.2.2.LI.4
Theme: ENERGY
Subtheme: WAVES
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This lesson explores a fascinating effect of light waves called refraction, which we observe every day. Have you ever noticed that a straight stick placed in a bucket of water appears bent at the water's surface? Or that the bottom of a clear river or swimming pool looks much shallower than it actually is? This is not a trick of the eye, but a real physical phenomenon. Today, we will investigate why this happens and derive a mathematical relationship to calculate this effect. Understanding this principle is crucial not just for passing exams, but for practical activities like fishing and for ensuring safety around bodies of water in our communities.
Teaching and Learning Resources: Basin/bowl, a 1 Ghana Cedi coin, water, a straight stick, projector, laptop, internet access for a simulation/video (if available). Starter Activity: The Magical Rising Coin (10 mins) Place a coin at the bottom of an empty, opaque bowl or basin. Ask a student to position their head so that the coin is just hidden from view by the rim of the bowl. While the student keeps their head perfectly still, slowly pour water into the bowl. Ask the student: "What do you observe?" (The student will be surprised to see the coin 'magically' appear in view). Class Discussion: Why did the coin become visible? The light rays from the coin must have bent at the water's surface to reach the student's eye. This bending of light is our topic for today: Refraction.
Part 1: Foundational Concepts (20 mins)
a) What is Refraction? Refraction is the bending of a wave (in our case, a light wave) as it passes from one medium to another medium of different optical density. Medium: A substance that light can travel through, e.g., air, water, glass. Optical Density: A measure of how much a medium slows down light. Water is optically denser than air. Glass is optically denser than water. Key Rule: When light travels from a less dense medium (like air) to a denser medium (like water), it bends towards the normal. When it travels from a denser medium (water) to a less dense medium (air), it bends away from the normal. The "normal" is an imaginary line perpendicular to the surface between the two media.
b) What is Refractive Index (n)? The refractive index of a medium is a number that tells us how much the speed of light is reduced in that medium compared to its speed in a vacuum (or air, for practical purposes). It has no units.