Waves and Optics
Lenses
To explain how converging and diverging lenses affect light and use ray diagrams to predict images.
What you will learn
How convex and concave lenses affect light
How to draw principal rays through lenses
How to locate an image using a ray diagram
How image size and orientation can change
The difference between real and virtual lens images
Explanation
A convex lens converges parallel rays to a principal focus; a concave lens diverges them as if from a focus. A convex lens can form real inverted images or, for an object inside the focal length, a virtual upright magnified image. A concave lens forms a virtual upright diminished image. Use principal rays and backward extensions to determine position and size. Example: State the image for an object inside a convex lens’s focal length. Virtual, upright and magnified. Give a reason. Compare cases.