First, let's recall the difference between a plane mirror and a curved mirror. A plane mirror reflects light straight back, giving an image that is the same size as the object. Curved mirrors, on the other hand, bend the reflected rays either inward or outward, which changes the size and orientation of the image. Notice the two types of curved mirrors listed here: concave and convex. A concave mirror curves inward, like the inside of a spoon, and can form real or virtual images depending on the object's position. A convex mirror bulges outward, like the rear‑view mirror in a car, and always produces a smaller, upright virtual image. By the end of this lesson, you will be able to identify concave and convex mirrors, explain how they form images, and state these learning objectives clearly. If anyone has a quick question before we move on, please raise your hand now.
Let's dive into concave mirrors, starting with the basic terminology you'll see on the slide. First, the principal axis is the straight line through the centre of curvature and the pole; the pole is the centre of the mirror's surface; the focus is the point where parallel rays converge; and the centre of curvature is the centre of the sphere of which the mirror is a part. Notice this diagram: the labels line up exactly with those parts we just defined. The curved surface reflects light toward the focus. About image formation: when an object is placed beyond the centre of curvature, the mirror creates a real, inverted image between the focus and the centre of curvature. If the object is between the focus and the pole, the image becomes virtual, upright, and larger, appearing behind the mirror. Any questions so far? Remember, a real image can be projected onto a screen, while a virtual image cannot.
Let's dive into convex mirrors – the basics. First, notice the principal axis, the pole, the virtual focus, and the virtual centre of curvature. These are similar to a concave mirror, but the focus and centre lie behind the mirror, so they're virtual. At this diagram: parallel rays strike the mirror and reflect outward, appearing to diverge from the virtual focus. Because the reflected rays never actually converge, any image formed is virtual, upright, and reduced in size – perfect for side‑view mirrors on cars. To recap: convex mirrors have a virtual focus and centre, produce upright reduced images, and are useful where a wide field of view is needed, like in Kenyan matatu rear‑view mirrors.
Let's learn how to draw ray diagrams for mirrors. We'll start with the basics and build step by step. First, remember we need at least two principal rays: the parallel ray, the ray through the focus, and the ray through the centre of curvature. Notice this shape here – it's the mirror surface where we'll place our object and draw the rays. Here's an example of a concave mirror ray diagram. Watch how the three rays converge at the image point. From the intersection we can determine the image location, its size, and whether it's real or virtual. Common mistakes include forgetting the focal ray or drawing rays on the wrong side of the mirror. Double‑check each ray as you go. If you follow these steps, you'll be able to sketch accurate ray diagrams for both concave and convex mirrors.
