Waves & Optics · Physics

Lenses create images by refraction through curved surfaces.

Learn converging vs diverging behavior, use the thin lens equation carefully, and connect ray diagrams to magnification and image type.

This topic

Thin Lenses and Image Formation

Use a consistent sign convention and an image “profile” (real/virtual, upright/inverted, magnified/reduced).

Types

Converging and diverging lenses

Converging lenses bring parallel rays toward a focal point; diverging lenses spread them out. Learn the qualitative behavior before doing calculations.

Parallel rays and focal point idea
Converging vs diverging intuition
Real vs virtual focus (conceptual)
Typical uses of each lens type

Equation

Thin lens equation

The thin lens equation links focal length, object distance, and image distance. The major skill is using consistent sign conventions and interpreting the result.

Object distance vs image distance meaning
Focal length sign conventions (intro)
Sanity checks for limiting cases
Connecting to ray diagram expectations

Size

Magnification

Magnification describes how image size compares to object size. The sign carries information about orientation (upright vs inverted).

Magnification as a ratio
Sign meaning (orientation)
When images are enlarged vs reduced
Relating magnification to distances

Tool

Ray diagrams

Ray diagrams are a reliable visual method for image location and type. Use a small set of principal rays consistently.

Principal rays for converging lenses
Principal rays for diverging lenses
How to locate real vs virtual images
Common diagram mistakes and fixes

Practice

Practice & Exercises

Practice lens ray diagrams, thin lens equation setups, and full image descriptions (type, orientation, size, location).

Ray diagram drills (converging/diverging)
Thin lens equation computation sets
Magnification sign and meaning questions
Real vs virtual classification practice
Exam-style lens problems