Module 5
1. Module 5
1.28. Page 5
Module 5—Wave Theory of Light
Lesson Summary
At the start of this lesson you were asked the following essential questions:
- What is a thin lens?
- How are ray diagrams used to predict image characteristics for thin lenses?
- How is the thin lens equation used to predict image characteristics for thin lenses?
In this lesson you learned that a thin lens is a circular piece of transparent material with a spherically shaped convex or concave surface. A converging lens has a convex surface that refracts rays parallel to the principal axis toward a focal point, producing a real image (assuming the object is farther than 1 focal length away from the lens). A diverging lens has a concave surface, refracting rays that are parallel to the principal axis outwards so that they appear to have originated from a virtual focal point, producing a virtual image.
Similar to ray diagrams for curved mirrors, many rays produce the image but only a few are required to identify its characteristics. A ray diagram with three or more rays can be used to accurately predict the image characteristics formed by both types of lenses.
The lens equation 
, which is identical to the curved mirror equation, can also be used to identify and predict image characteristics. Human vision is a good example of an optical system that can involve multiple lenses causing precise amounts of refraction to produce a clear image on the retina of the observer.
Lesson Glossary
converging lens: a lens that refracts rays travelling parallel to the principal axis inward to the focal point of the lens
diverging lens: a lens that refracts rays travelling parallel to the principal axis outward so that they appear to have originated or passed through the virtual focal point of the lens
thin lens equation: an equation that relates image distance, object distance, and the focal length of a thin lens