Overview
This lecture explains the properties, equations, and image formation for concave and convex mirrors, including sign conventions, ray diagrams, magnification, and examples.
Mirror Types and Parts
- Concave mirrors curve inward; convex mirrors curve outward.
- The principal axis is the central horizontal line through the mirror.
- The center of curvature (C) is the center of the mirror's circular shape.
- The radius of curvature (R) is the distance from the center to the mirror's surface.
- The focal point (F) is halfway between the mirror and the center of curvature.
- Focal length (f) = ½ radius of curvature (f = R/2).
Sign Conventions
- Object distance (do) is positive if in front of the mirror (real object); negative if behind (virtual object).
- Image distance (di) is positive if in front of the mirror (real image); negative if behind (virtual image).
- Focal length for concave mirrors is positive; for convex mirrors, it's negative.
Mirror and Magnification Equations
- Mirror equation: 1/f = 1/do + 1/di
- Magnification (M) = hi/ho = –di/do
- M > 0: image is upright.
- M < 0: image is inverted.
- |M| > 1: image is enlarged.
- |M| < 1: image is reduced.
Image Formation by Concave Mirrors
- Object beyond center: image is real, inverted, and reduced.
- Object at center: image is real, inverted, same size.
- Object between center and focus: image is real, inverted, enlarged.
- Object at focus: no image forms (image at infinity).
- Object between mirror and focus: image is virtual, upright, enlarged, and behind the mirror.
Image Formation by Convex Mirrors
- Focal length is negative.
- Images are always virtual, upright, and reduced, located behind the mirror.
Ray Diagram Summary
- Parallel ray reflects through focal point (concave) or appears to diverge from focal point (convex).
- Ray through center reflects back on itself.
- Use ray diagrams and sign conventions to determine image properties.
Key Terms & Definitions
- Concave mirror — mirror with inward-curved surface.
- Convex mirror — mirror with outward-curved surface.
- Principal axis — central horizontal line through the mirror.
- Center of curvature (C) — center of the circle that forms the mirror.
- Focal point (F) — point where parallel rays meet or appear to meet after reflection.
- Focal length (f) — distance from mirror to focal point.
- Object distance (do) — distance from object to mirror.
- Image distance (di) — distance from image to mirror.
- Magnification (M) — ratio of image height to object height.
Action Items / Next Steps
- Practice solving mirror equation and magnification problems.
- Draw ray diagrams for different object positions.
- Memorize sign conventions for mirror equations.