1. PHY138 – Waves, Lecture 9 Today’s overview Lenses The Thin Lens Equation Lenses Used in Combination

2. It’s the last week of the fall semester! The last Waves Problem Set is due at 5:00 PM today in your TA’s mailbox. There is no Web-CT quiz until Jan.3. There is a practice www.masteringphysics.com assignment now available (not due) on Chapter 26 material.

3. Announcements: Test 2 is at 9:00 AM sharp on Friday Dec. 10. You will need:  A non-programmable calculator  An aid sheet with the main equations used this quarter, and other info you think might be useful. It may be double-sided, up to 8½×11” in size. It must be hand-written; no shrink photocopies or condensed type! Room Assignments are now listed on the course web-site.

4. A fish swims directly below the surface of the water. An observer sees the fish at: 1. a greater depth than it really is. 2. its true depth. 3. a smaller depth than it really is. air water Quiz 1

5. Light going through a prism bends toward the base

6. Building a Converging Lens out of Prisms Snell’s Law of Refraction is obeyed at every interface.

7. Converging Lens Focal Point Focal length, f NOTE: Focal length is defined for initially parallel rays.

8. Diverging Lens Virtual Focal Point Negative Focal length, - f Rays appear to emerge from Virtual Focal Point

9. Off-axis rays through a converging lens Focal length, f NOTE: The ray which passes through the centre of the lens is not bent.

10. Diverging rays through a Converging Lens Focal length, f This follows from the principle of reversibility.

11. Quiz 2 f What will happen to the rays emerging to the right of the lens if the face is moved a little closer to the lens? 1.They will remain parallel. 2.They will diverge (spread out). 3.They will converge (toward a focus).

12. Quiz 3 f What will happen to the rays emerging to the right of the lens if the face is moved a little further away from the lens? 1.They will remain parallel. 2.They will diverge (spread out). 3.They will converge (toward a focus).

13. Diverging rays through a Converging Lens Focal length, f p q

14. Thin Lens Equation: sign conventions p q f object image p is positive for objects to the left of lens, negative for objects to the right of lens (virtual objects). q is positive for images to the right of lens, negative for images to the left of lens (virtual images). f is positive for converging lenses, negative for diverging lenses.