2. Lenses A transparent object used to change the path of light Examples: Human eye Eye glasses Camera Microscope Telescope Reading stones used by monks, nuns, and scholars ~1000 C.E.

3. Lenses THERE ARE ALWAYS TWO REFRACTIONS IN A LENS

4. Lenses Two basic shapes Converging lens Diverging lens

5. Converging Lens A lens that has its thickest part in the middle Causes all incident parallel rays to converge at a single point after refraction

6. Converging Lens OPTICAL CENTRE: the exact centre of the lens

7. Ray diagrams for Converging Lenses

9. Images through Converging Lenses Let’s practice

10. Images in Convex lens vu f Image Real, inverted & highly diminished Image formed in convex lens when the object is placed at infinity FF 2F Use As a camera lens when object is very far, burning lens

11. object Images in Convex lens vu f Image Real, inverted & diminished Image formed in convex lens when the object is placed beyond 2f FF 2F Use As a camera lens when object is not very far

12. Image formed in convex lens when the object is placed at 2f object Image Real, inverted & same size as object Images in Convex lens vu f FF 2F Use In terrestrial telescope for erecting the image

13. Image formed in convex lens when the object is placed between f and 2f object Image Real, inverted & magnified Images in Convex lens vu f FF 2F Use Cinema and slide projectors

14. Image formed in convex lens when the object is placed at the focus object Image At Infinity, inverted and highly magnified Images in Convex lens u f FF 2F Use In collimator of a spectrometer to obtain parallel beam

15. Image formed in convex lens when the object is placed between the Focus and optical centre object Images in Convex lens u f Image Virtual, magnified & upright FF 2F Use As a reading glass

16. Converging Lenses Can produce real and virtual images The size and attitude will vary depending on the location of the object Many uses including to correct for far-sightedness LocationSizeAttitudeLocationType Beyond 2F ’ SmallerInvertedBehindReal At 2F ’ SameInvertedBehindReal Between 2F ’ and F ’ LargerinvertedBehindReal At F ’ No clear image Inside F ’ largeruprightIn frontVirtual Object Image -------------------------------------------- ---

17. Diverging Lens A lens that has its thinnest part in the middle Causes all incident parallel light rays to spread apart after refraction

18. Diverging Lens

19. Ray diagrams for Diverging Lenses

21. Images through Diverging Lenses Let’s practice

22. Diverging Lenses Only produce virtual images that are always smaller, upright and in front of the lens Used to correct near-sightedness (can see objects close up)

23. Image formed in concave lens when the object is placed at infinity Images in Concave lens Image Virtual, erect & diminished f FF 2F Use In Galilean telescope

24. Image formed in concave lens when the object is placed in front of lens object Images in Concave lens Image Virtual, erect & diminished v u f FF 2F Use In spectacles for correcting short-sightedness

25. Applications of Lenses

26. Cornea Iris Pupil Lens Optic nerve Retina Suspensor ligament

27. 27

28. 28

29. 29

30. 30

31. 31