# Lesson Plan: Convex Lenses Physics

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to define convex lenses, describe the paths of light rays refracted through these lenses, and explain how rays are focused by such lenses.

#### Objectives

Students will be able to

• qualitatively describe convexity of a lens (thick in the middle and thin at the edges and has a smooth curvature),
• identify the changes in the direction of travel of light rays as they enter and as they exit a convex lens at different distances perpendicular to the optical axis of the lens,
• explain that the change in the light ray travel direction is due to refraction and so depends on the material that the lens is made of,
• demonstrate that parallel rays entering a convex lens converge at a focus point that is on the side of the lens that the rays exit from,
• recall that the distance between the center of the lens and the point that parallel incident rays converge at is called the focal length,
• recall that the power of a lens is the reciprocal of its focal length.

#### Prerequisites

Students should already be familiar with

• the fact that light rays travel in straight lines,
• the fact that a light ray’s direction of travel changes due to refraction at an optical boundary.

#### Exclusions

Students will not cover

• any calculations,
• formation of images,
• any lens shape other than convex.