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: 14
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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This lesson is part of our study of Waves, focusing on the behaviour of light waves. We have already learned that light travels in straight lines and can be reflected. Today, we will investigate a fascinating phenomenon: what happens when we place an object not in front of one, but *between two* plane mirrors that are joined at an angle. This setup creates multiple reflections, leading to the formation of several images. Understanding this principle is key to applications we see every day, from the local barbershop to advanced optical instruments. We will conduct a hands-on activity to discover the rule that governs this effect and then apply it mathematically.
A. Recap: Reflection in a Single Plane Mirror Before we look at two mirrors, let's remember the characteristics of an image formed by a single plane mirror: The image is virtual (it cannot be formed on a screen). The image is erect (upright). The image is the same size as the object. The image is laterally inverted (left and right are swapped). The distance of the image from the mirror is equal to the distance of the object from the mirror. B. Multiple Reflections in Inclined Mirrors When two plane mirrors are joined at an angle (inclined), light from an object can reflect off one mirror and then off the second mirror. The image formed by the first mirror acts as a virtual object for the second mirror, which then forms another image. This process can continue, creating multiple images.
Imagine you are standing between two mirrors in a fitting room. Light from you hits Mirror 1, forming Image 1. Light from you also hits Mirror 2, forming Image 2. Now, the light that formed Image 1 can travel towards Mirror 2, and Mirror 2 will form an image *of Image 1*. This becomes Image 3. Similarly, the light that formed Image 2 travels to Mirror 1, which forms an image *of Image 2*. This becomes Image 4. This process of images-of-images continues until the light ray can no longer strike another mirror surface. All the images formed lie on a circle whose centre is the point where the mirrors meet. C. The Formula for Calculating the Number of Images Through observation and experiment (which we will do in our activity), physicists have derived a simple formula to predict the number of images formed.
The number of images, n, formed by two plane mirrors inclined at an angle θ (theta) is given by:
`n = (360° / θ) - 1`