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.3
Strand code: 2
Sub-strand code: 2
Content standard code: 1.2.2.CS.2
Indicator code: 1.2.2.LI.3
Theme: ENERGY
Subtheme: WAVES
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We interact with mirrors every day, from the small mirror we use to check our appearance to the side mirrors on a *trotro* or an Uber. These are not all flat (plane) mirrors; many are curved. These curved or spherical mirrors play a crucial role in technology and safety. For instance, the side mirror of a car helps the driver see more of the road, preventing accidents. A satellite dish, like the ones used for DStv or MultiTV, is a type of curved mirror that collects signals. Understanding how these mirrors work mathematically allows us to predict where an image will form, how large it will be, and what it will look like.
A. Recap of Spherical Mirror Terminology
Before we use the formulas, let's remember the key parts of a spherical mirror: Concave Mirror (Converging Mirror): Curls inward, like the inside of a spoon. It converges parallel rays of light to a point. Convex Mirror (Diverging Mirror): Bulges outward, like the back of a spoon. It diverges parallel rays of light so they appear to come from a point behind the mirror. Object Distance (u): The distance from the pole (centre) of the mirror to the object. Image Distance (v): The distance from the pole of the mirror to the image. Focal Length (f): The distance from the pole of the mirror to the principal focus (F). For a spherical mirror, the focal length is half the radius of curvature (`f = R/2`). B. The Sign Convention: "Real is Positive"
This is the most important rule for using the mirror formulas correctly. It helps us translate a physical situation into a mathematical equation. We will use the "Real is Positive" convention, which is very intuitive.
| Quantity | When it is POSITIVE (+) | When it is NEGATIVE (-) | | :--- | :--- | :--- | | Object Distance (u) | Always positive for a single real object placed in front of the mirror. | (Not applicable at SHS1 level) | | Image Distance (v) | Image is REAL (formed in front of the mirror, where light actually converges). Real images can be projected onto a screen. | Image is VIRTUAL (formed behind the mirror, where light only *appears* to come from). Virtual images cannot be projected. | | Focal Length (f) | For a CONCAVE (converging) mirror. | For a CONVEX (diverging) mirror. | | Magnification (m) | Image is UPRIGHT (and therefore virtual). | Image is INVERTED (and therefore real). | | Image Height (h_i) | Image is UPRIGHT. | Image is INVERTED. |