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: 16
Grade code: 1.2.2.LI.1
Strand code: 2
Sub-strand code: 2
Content standard code: 1.2.2.CS.2
Indicator code: 1.2.2.LI.1
Theme: ENERGY
Subtheme: WAVES
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Welcome, future scientists and engineers! Today, we are exploring the fascinating world of spherical mirrors. These are not the flat (plane) mirrors we use every day to check our uniforms. Think about the shiny outer surface of a large soup ladle, the side mirror of a "trotro" or a taxi, or the mirrors used by dentists. These are all examples of curved or spherical mirrors. Understanding how they work is fundamental to optics and has applications all around us, from our homes to advanced technology. By the end of this lesson, you will be able to predict and draw exactly how these mirrors form images.
This section contains the core content you will need to master. We will break it down step-by-step. A. Types of Spherical Mirrors
A spherical mirror is a mirror which has the shape of a piece cut out of a spherical surface. There are two types: Concave Mirror (Converging Mirror): The reflecting surface is curved inwards, like the inside of a bowl or a cave. It is called a converging mirror because it causes parallel rays of light to converge (come together) at a point. *Memory Aid:* Concave has "cave" in it - the reflecting surface goes inwards. Convex Mirror (Diverging Mirror): The reflecting surface is curved outwards, like the back of a spoon. It is called a diverging mirror because it causes parallel rays of light to spread out or diverge as if they are coming from a point behind the mirror. B. Important Terms and Definitions
To draw ray diagrams accurately, we must understand the language of mirrors. Pole (P): The geometric centre of the reflecting surface of the mirror. It is the midpoint of the mirror itself. Centre of Curvature (C): The centre of the sphere of which the mirror is a part. For a concave mirror, C is in front of the mirror. For a convex mirror, C is behind the mirror. Radius of Curvature (R): The distance from the Pole (P) to the Centre of Curvature (C). It is the radius of the sphere from which the mirror was cut. Principal Axis: The straight line passing through the Pole (P) and the Centre of Curvature (C). Principal Focus (F): For a concave mirror, it is the point on the principal axis where rays of light initially parallel to the principal axis converge (meet) after reflection. For a convex mirror, it is the point on the principal axis from which rays of light initially parallel to the principal axis appear to diverge (spread out) after reflection. Focal Length (f): The distance from the Pole (P) to the Principal Focus (F).
Crucial Relationship: The Principal Focus (F) is located exactly halfway between the Pole (P) and the Centre of Curvature (C). Therefore, the focal length is half the radius of curvature: f = R / 2 or R = 2f. C. The Rules of Ray Tracing