1. Refraction & lenses

2. Types Of Lenses

3. Image Formation via Refraction by thin lenses Thin lenses are those whose thickness is small compared to their radius of curvature. They may be either converging (a) or diverging (b). CONVEX=Converging (+)LENS CONCAVE=Diverging (-) LENS

4. Converging Lenses (aka Positive or Convex lenses) Parallel rays are brought to a focus by a converging lens (one that is thicker in the center than it is at the edge).

5. Convex Lenses Thicker in the middle than at the edges. –Often called a converging lens because it refracts parallel light rays so that they meet at a single point. –Focal point is on the opposite side of the lens, so the focal length is positive. Focal Point

6. Refraction by a converging lens

7. Diverging Lenses (aka Negative or Concave lenses) A diverging lens (thicker at the edge than in the center) make parallel light diverge; the focal point is that point where the diverging rays would converge if projected back.

8. Refraction in a diverging lens

9. Converging and diverging lens

10. Convex lens: Ray Tracing

11. The Formation of Images by Lenses RAY DIAGRAMS

12. Thin lens approximation

13. A 6 cm high object is placed 8 cm from a convex lens with a focal length of 5 cm. Use ray tracing to locate the image.

14. Ray Tracing: Convex Lens For a diverging lens, we can use the same three rays; the image is upright and virtual.

15. Simulation http://phet.colorado.edu/sims/geometric- optics/geometric-optics_en.html

16. Converging lens simulation

17. Diverging lens simulation

18. The Formation of Images by Lenses IMAGE FORMATION BY A CONVERGING LENS In this example, when the object is placed further than twice the focal length from the lens, the real image is inverted and smaller than the object.

19. The Camera Aperture size determined by number expressing it as a ratio of focal length to opening called f-number

20. The Thin-Lens Equation and the Magnification Equation

21. Example: The Real Image Formed by a Camera Lens A 1.70-m tall person is standing 2.50 m in front of a camera. The camera uses a converging lens whose focal length is 0.0500 m. (a)Find the image distance and determine whether the image is real or virtual. (b) Find the magnification and height of the image on the film. (a) real image (b)

22. Example A stamp collector uses a converging lens with focal length of 24 cm to view a stamp 18 cm in front of the lens. A) where is the image located b) what is the magnification

23. Example A bright object and a viewing screen are separated by a distance of 66.0 cm. At what location ( s) between the object and the screen should a lens of focal length 12.5 cm be placed in order to produce a crisp image on the screen. ( hint: first draw a diagram)

24. Example What is the location and size of the image of a 5 cm high object that is located: A) 10 cm from a converging lens with a focal length of 5 cm B) 3 cm from a converging lens with a focal length of 5 cm C) 8 cm from a converging lens with a focal length of 5cm D) 20 cm from a diverging lens with a focal length of 5 cm

25. 26.9 Lenses in Combination The image produced by one lens serves as the object for the next lens.

26. The Eye The camera is modeled after the eye “Normal” reading distance is 25 cm Eye is about 2.5 cm in diameter Most of focusing is done by the cornea and vitreous humor behind the cornea

27. 26.10 The Human Eye ANATOMY

28. 26.10 The Human Eye OPTICS The lens only contributes about 20-25% of the refraction, but its function is important.

29. Myopia Correct for the far point Power of lens Lens powers add

30. Hyperopia Correct for the near pointCorrect for the near point

31. 26.10 The Human Eye NEARSIGNTEDNESS The lens creates an image of the distance object at the far point of the nearsighted eye.

32. 26.10 The Human Eye FARSIGNTEDNESS The lens creates an image of the close object at the near point of the farsighted eye.

33. 26.10 The Human Eye THE REFRACTIVE POWER OF A LENS – THE DIOPTER Optometrists who prescribe correctional lenses and the opticians who make the lenses do not specify the focal length. Instead they use the concept of refractive power.

34. Optical instruments http://www.physchem.co.za/OB11- wav/instruments.htmhttp://www.physchem.co.za/OB11- wav/instruments.htm students to analyze one instruments and explain the working of the instrument with ray diagram

35. 26.14 Lens Aberrations In a converging lens, spherical aberration prevents light rays parallel to the principal axis from converging at a single point. Spherical aberration can be reduced by using a variable-aperture diaphragm.

36. 26.14 Lens Aberrations Chromatic aberration arises when different colors are focused at different points along the principal axis.