1. Curved Lenses SNC2P – Optics

2. Lenses Lenses are thin pieces of glass or plastic that have at least one curved side. There are two basic types of lenses: convex (converging – cause light rays to be refracted toward the principal axis)

3. Lenses Lenses are thin pieces of glass or plastic that have at least one curved side. concave (diverging – cause light rays to be refracted away from the principal axis).

4. From our lesson and demos on refraction we know that light bends when it enters and exits a material. For our purposes, we will understand that lenses are very thin and assume that light refracts only once in the material, at the axis of symmetry.

5. Important Terms Principal axis - a straight line that passes through the optical centre, O. Focal point (lenses have 2 because light can pass through in either direction) The point where light rays converge after refraction is designated the principal focal point - F The focal point on the other side of the lens is designated the secondary focal point - F’ (“F prime”). If light were coming from the other direction, F and F’ would be reversed. Optical centre (O) – centre of lens (vertically and horizontally) Axis of symmetry – vertical line through optical centre

6. Diagrams

7. Finding Images in Lenses – The Rules Lens Rules: Convex (Converging) Lenses Rules for drawing ray diagrams: 1.A light ray travelling parallel to the principal axis is refracted through the principal focus, F. 2.A light ray travelling toward the secondary focus, F’, refracts parallel to the principal axis. 3.A light ray that passes through the optical centre goes straight through, without refracting.

8. Examples

14. Finding Images in Lenses – The Rules Lens Rules: Concave (Diverging) Lenses Rules for drawing ray diagrams: 1.A ray parallel to the principal axis is refracted as if it had come through the principal focus (F). 2.A ray that appears to pass through the secondary principal focus (F ’ ) is refracted parallel to the principal axis. 3.A ray through the optical centre (O) continues straight through on its path.

15. All images using diverging lenses have the same characteristics

16. Homework Complete the lenses drawing practice sheet