Unit 2 - Lesson 1: Plane and Spherical Mirrors

Light reflection is defined as the bouncing back of light rays into the same medium when they strike a reflecting surface. This fundamental optical behavior is governed by two immutable physical laws: 1. (First Law of Reflection): [Angle of Incidence = Angle of Reflection]. If a ray strikes at an angle of 40°, it reflects precisely at 40°. When a ray falls perpendicularly on a reflecting surface, its angle of incidence is 0°, causing it to reflect directly back on itself. 2. (Second Law of Reflection): [The incident ray, the reflected ray, and the normal to the reflecting surface at the point of incidence all lie in one plane perpendicular to the reflecting surface].

When an object stands in front of a flat (Plane Mirror), the resulting image exhibits five consistent characteristics: 1. (Upright / Erect): The image orientation matches the object vertically (head up, feet down). 2. (Equal in Dimensions): The image size is exactly identical to the true object size (neither magnified nor diminished). 3. (Virtual): It cannot be received on a physical projection screen because it is formed by the intersection of the extensions of reflected rays behind the mirror. 4. (Laterally Inverted): Right appears left and left appears right. Consequently, the word 'AMBULANCE' is painted laterally inverted on the front of emergency vehicles so drivers ahead can read it upright in their rearview mirrors and yield. 5. (Distance Equivalence): The distance from the object to the mirror strictly equals the distance from the mirror to the virtual image. If you stand 3 meters from a mirror, your image is 3 meters behind the mirror, creating a total distance of 6 meters between you and your image.

A (Spherical Mirror) is defined as a mirror whose reflecting surface forms part of a hollow sphere. Spherical mirrors are divided into two fundamental types: 1. (Concave / Converging Mirror): Its reflecting surface is the interior surface of the hollow sphere. It gathers (converges) incident parallel rays after reflection into a single point called the (Real Focus). 2. (Convex / Diverging Mirror): Its reflecting surface is the exterior outer surface of the hollow sphere. It scatters (diverges) incident parallel rays upon reflection so that only their extensions intersect behind the mirror at a (Virtual Focus).

To analyze spherical mirrors geometrically, six foundational parameters must be mastered: 1. (Center of Curvature, C): The center of the hollow sphere of which the mirror is a part. 2. (Pole of Mirror, P): An imaginary point located at the geometric center of the reflecting surface. 3. (Radius of Curvature, r): The radius of the sphere, or the distance between the center of curvature and any point on the reflecting surface (distance CP). 4. (Principal Axis): The unique straight line passing through the pole of the mirror and its center of curvature. 5. (Secondary Axis): Any straight line passing through the center of curvature and any point on the reflecting surface except the pole. 6. (Principal Focus, F) and (Focal Length, f): The focal length is the distance between the pole and the principal focus (FP). Crucial rule: [r = 2 × f]; the radius of curvature equals twice the focal length.