1. Chapter 13: Lenses and Optical Devices
13.1 Lenses and the Formation of Images

2. Basic Lens Shapes There are two basic shapes of lenses:
Concave Lenses (Diverging)
Convex Lenses (Converging)

3. Types of Lenses

4. Converging Lens Diverging Lens
Parallel light rays converge through a single point after they travel through the lens.
Lens is thickest in the middle
Diverging Lens
Parallel light rays diverge after they travel through the lens.
Lens is thickest at the edge

5. Lenses use Refraction
Light is refracted twice as it passes through a lens: once from air to glass, and once from glass to air.
Ray diagrams are simplified by drawing a dashed line through the center of the lens and showing refraction occurring at this line.

6. Diverging Concave Lens

7. terminology
Axis of Symmetry: imaginary vertical line drawn through the optical centre perpendicular to the principal axis (through the middle of the lens)
Optical centre: point where the axis of symmetry meets the principal axis
Principal focus: where all the rays meet.
Secondary principal focus: point on the other side of the lens equal in distance from the principal focus.

8. Click on this hyperlink to see a diverging lens in action

9. Diverging (Concave) Lenses
Light rays of a diverging lens do not converge. If you project these diverging rays backwards, it looks as if they come from a virtual focus.

10. Uses of Concave Lenses Images formed are smaller, virtual and upright.
Some types of eyeglasses and telescopes use concave lenses along with convex lenses (which are more useful)

11. Converging (Convex) Lens

12. Click on this hyperlink to see converging lens in action

13. Ray Diagrams with Converging Lenses
Table 11.7 on p. 453
1)Copy this table into your notebook (includes uses)
2)Copy the steps for drawing a convex lens ray diagram on page 454 in your notebook.

14. Homework / Classwork
P #1-4