Lesson Notes By Weeks and Term v4 - SHS 1
WAVES
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
WAVES
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Physics
Class: SHS 1
Term: 1st Term
Week: 17
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
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
This lesson explores how curved or spherical mirrors form images. Unlike the flat (plane) mirrors we use every day to check our appearance, spherical mirrors can make things look bigger, smaller, or even upside down. We see them everywhere in Ghana – from the side mirrors of a *trotro* or an Uber, to the security mirrors in supermarkets like Melcom, and even in solar cookers used in some communities. By understanding how light waves reflect off these curved surfaces, we can understand the technology behind these useful tools. This lesson will focus on a graphical method called ray tracing to predict and describe the images formed.
A. Introduction to Spherical Mirrors
A spherical mirror is a mirror which has the shape of a piece cut out of a spherical surface. Imagine a hollow glass ball. If we cut a piece of it and coat one side with a reflective material (like silver), we get a spherical mirror.
There are two types of spherical mirrors: Concave Mirror (Converging Mirror): The reflecting surface is curved inwards, like the inside of a spoon. It is called a converging mirror because it gathers (converges) parallel rays of light to a single point. Convex Mirror (Diverging Mirror): The reflecting surface is curved outwards, like the back of a spoon. It is called a diverging mirror because it spreads out (diverges) parallel rays of light that strike it. The rays appear to come from a single point behind the mirror. B. Terminology for Spherical Mirrors
To draw and understand ray diagrams, we must know the language of mirrors. Pole (P): The geometric centre of the mirror's reflecting surface. Centre of Curvature (C): The centre of the sphere from which the mirror was cut. Any line drawn from C to the mirror is normal (perpendicular) to the mirror's surface at that point. Radius of Curvature (R): The distance from the Pole (P) to the Centre of Curvature (C). `R = PC`. 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 axis converge (meet) after reflection. It is a *real focus*. For a convex mirror, it is the point on the principal axis from which parallel rays of light *appear to diverge* after reflection. It is a *virtual focus* and is located behind the mirror. Focal Length (f): The distance from the Pole (P) to the Principal Focus (F). `f = PF`.