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: 12
Grade code: 1.2.2.LI.3
Strand code: 2
Sub-strand code: 2
Content standard code: 1.2.2.CS.1
Indicator code: 1.2.2.LI.3
Theme: ENERGY
Subtheme: WAVES
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Good morning, class! Today, we are continuing our study of waves, specifically focusing on the behaviour of light waves. We all use mirrors every day to check our appearance. But have you ever been to a barber's shop or a tailor's shop and seen multiple reflections of yourself? You might see your back in the mirror in front of you. This happens because they use more than one mirror. This phenomenon is called multiple reflection.
Concept 1: What are Inclined Mirrors? When two plane mirrors are placed with their reflecting surfaces facing each other such that they make an angle (`θ`) between them, they are called inclined mirrors. An object placed between them will have multiple images formed due to repeated reflections of light waves between the two mirrors. An image formed in Mirror 1 can act as a virtual object for Mirror 2. Similarly, an image formed in Mirror 2 can act as a virtual object for Mirror 1. This process continues, creating a series of images that appear to lie on the circumference of a circle. Concept 2: The Relationship Between Angle and Number of Images (Guided Discovery) Let's investigate this relationship as scientists do—through experimentation.
Activity (as per NaCCA exemplar): Form groups of 4-5 students (mixed-ability). Take two plane mirrors and join them along one edge with tape so they can be opened like a book. Place the mirrors on a sheet of paper. Use a protractor to set the angle `θ` between the mirrors. Place a small object (like a coin) symmetrically between the mirrors. Look into the mirrors and carefully count the total number of images you can see.
Expected Observations and Analysis:
| Angle of Inclination (`θ`) | Number of Images Observed (`n`) | Calculation: `(360° / θ)` | | :------------------------- | :------------------------------ | :-------------------------- | | 90° (for a start) | 3 | `360 / 90 = 4` | | 60° | 5 | `360 / 60 = 6` | | 45° | 7 | `360 / 45 = 8` | | 30° | 11 | `360 / 30 = 12` |