Lesson Notes By Weeks and Term v4 - SHS 1
WAVES
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Subject: Physics
Class: SHS 1
Term: 1st Term
Week: 20
Grade code: 1.2.2.LI.2
Strand code: 2
Sub-strand code: 2
Content standard code: 1.2.2.CS.2
Indicator code: 1.2.2.LI.2
Theme: ENERGY
Subtheme: WAVES
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Welcome, future scientists and engineers! Today, we are exploring a fascinating property of light that you see every day but might not have a name for. Have you ever put a straw in a glass of water or *sobolo* and noticed it looks bent or broken at the water's surface? Or have you looked into a clear river or bucket of water and thought the bottom looked closer than it really was? This is not a trick of your eyes; it is a real physical phenomenon called refraction. Refraction is the bending of light as it passes from one material (like air) into another (like water or glass).
This section breaks down the core ideas we need to understand refraction. A. What is Refraction?
Refraction is the bending of a wave (in our case, light) as it passes from one medium to another medium where its speed is different. Medium: A substance that a wave travels through (e.g., air, water, glass, diamond). Why does it bend? Light does not travel at the same speed in all materials. It travels fastest in a vacuum (and very nearly as fast in air) and slows down when it enters denser materials like water or glass. This change in speed is what causes the light to bend or change direction.
Analogy: Imagine you are pushing a lawnmower from a smooth pavement onto a thick, grassy lawn at an angle. The right wheel hits the grass first and slows down, while the left wheel is still on the pavement moving fast. This difference in speed will cause the entire lawnmower to turn. Light behaves in a similar way. B. Key Terms and Definitions
To discuss refraction properly, we must use specific terms. Let's look at a diagram of light entering a glass block from the air. Incident Ray: The ray of light travelling in the first medium (air) that strikes the boundary. Point of Incidence: The point where the incident ray strikes the boundary between the two media. Normal: An imaginary line drawn perpendicular (at 90°) to the surface at the point of incidence. This is our reference line for all angles. Refracted Ray: The ray of light that has passed through the boundary and is now travelling in the second medium (glass). Angle of Incidence (i): The angle between the incident ray and the normal. Angle of Refraction (r): The angle between the refracted ray and the normal. Optically Denser Medium: A medium in which light travels more slowly (e.g., glass, water). Light bends towards the normal when entering an optically denser medium. Optically Rarer Medium: A medium in which light travels faster (e.g., air). Light bends away from the normal when entering an optically rarer medium. C. The Laws of Refraction