InClass

1. High School Optics PHYSICS InClass by SSL Technologies with S. Lancione Exercise-52 Lenses Part 1 /2

2. Concave Convex Lenses PART-1 /2 LENSES Whereas mirrors produce images by reflection, lenses produce images by refraction. Depending upon their “thickness”, lensesare classified as “thick” or “thin”. In this course, we will onlyconsider “thin” lenses. In effect, therefore, we disregard thethickness of the lens assuming it to be a line. Click

3. Lenses PART-1 There are two main types of lenses called convex (also knownas converging) and concave(also known as diverging). Convex lenses are thicker in the middle than at the edges while concave lenses are thicker at the edges than in the middle. As illustrated below, both convex and concave lenses each have three variations. Click

4. Convex Lens Concave Lens Lenses PART-1 When representing “thin” lenses in a diagram, it is sometimes more convenient to simply draw an arrow rather than the actual lens. Using this method, an arrow is used to represent the lens as illustrated below. Click

5. REMEMBER Convex lenses are thicker in the middle and thus converge light rays. Concave lenses are thinner in the middle and thus diverge light rays. Click

6. Lenses PART-1 Just as with concave mirrors, the characteristics of the image formed by a converging lens depend upon the location of the object. There are six "strategic" locations where an object may be placed. For each location, the image will be formed at a different place and with different characteristics. We will illustrate the six different locations and label them as CASE-1 to CASE-6. Case-1: Object at infinity Case-2: Object just beyond 2 F’ Case-3: Object at 2F’ Case-4: Object between 2F’ and F’ Case-5: Object at F’ Case-6: Object within focal length (f) Click

7. Convex (converging) Lenses Infinity simply means “far away”. CASE-1: Object at “infinity” No image Object NOTE Since the object is at “infinity”, all rays arrive parallel. No image formed(All rays pass through F) Click

8. Note-1 A ray that comes parallel is refracted through F. Note-2 A ray that goes through the vertex goes right through. Note-3 A ray that goes through F’ is refracted parallel. This ray is extrain locating theimage. Convex (converging) Lenses NOTE In order to establishan image point, allwe need are twointersecting rays. CASE-2: Object just beyond 2F’ Object Image Image is real (formed by refracted rays) Inverted (upside down) Reduced (smaller than object) Located between F and 2F Click

9. This ray is extra. Convex (converging) Lenses Again: In order to establishan image point, allwe need are twointersecting rays. CASE-3: Object at 2F’ Image Object Image is real (formed by refracted rays) Inverted (upside down) Same size as object Located at 2F Click

10. Convex (converging) Lenses CASE-4: Object between 2F’ and F’ Object Image Image is real (formed by refracted rays) Inverted (upside down) Magnified (larger than object) Located beyond 2F Click

11. Convex (converging) Lenses CASE-5: Object at F’ No image Object No image is formed (rays refract parallel) Click

12. Convex (converging) Lenses CASE-6: Object is within focal length Image Object Image is virtual (formed by extended rays) Upright Magnified Located on same side as object Click

13. Now let's consider Concave lenses delay

14. Concave (diverging) Lenses One case only! Object Image Image is always virtual (formed by a direct ray and an extended ray) Always upright Always reduced Always located on same side as object Click

15. Lenses PART-1 Be sure to follow the following sign convention whensolving problems concerning lenses. Sign convention: 1- Object distance is always positive. 2- Image distance is positive if the image is on the side of the lens where light emerges (from lens). 3- Image distance is negative if the image is on the side of the lens where the light enters (the lens). 4-The focal length of a convex (converging) lens is positive. 5- The focal length of a concave (diverging) lens is negative. Click

16. EXERCISES

17. Question-1 A lens or a lens. A lens that is thickerin the middle than at the ends is known as: Convex Converging Click Click

18. Question-2 A lens or a lens. A lens that is thickerat the ends than in the middle is known as: Concave Diverging Click Click

19. Question-3 Trace the rays that emerge from the following glass mediums: a) b) c) d) Click Click

20. Question-4 For each case below, draw the appropriate lens that will produce the indicated rays. a) Concave (diverging) b) Convex (converging) Click Click

21. Question-5 How is the image formed by a mirror different from the image formed by a lens? A mirror forms an image by reflection whereas a lens forms a an image by refraction. Click Click

22. Question-6 For each convexlens illustrated below, draw the image. a) Image Image is real, inverted, reducedand located between F and 2F. Click Click

23. Question-6 For each convexlens illustrated below, draw the image. b) Image Image is real, inverted, samesize object and located at 2F. Click Click

24. Question-6 For each convexlens illustrated below, draw the image. c) Image Image is real, inverted, magnifiedand located beyond 2F. Click Click

25. Question-6 For each convexlens illustrated below, draw the image. d) Parallel All rays refract parallel, no image is formed. Click Click

26. Question-6 For each convexlens illustrated below, draw the image. e) Image Image is virtual, upright, magnifiedand located on same side as object. Click Click

27. Question-7 For each concavelens illustrated below, draw the image. REMEMBER Concave lenses always produce imagesthat are virtual, upright and reduced. Image Image is virtual, upright, reducedand located on same side as object. Click Click

28. Question-7 For each concavelens illustrated below, draw the image. Image Image is virtual, upright, reducedand located on same side as object. Click Click

29. Question-8 Negative sign indicates inversion. An object that is 7 cm high is placed 20 cm in front of a convex(converging) lens whose focal length is 15 cm. Determine the characteristics of the image: Real Type (real or virtual): _______________ Location: _______________ Magnification: _______________ Height: _______________ 60 cm -3 (inverted and 3x larger than object) 21 cm Click Click

30. Question-9 Note that diverging lenseshave a negative focal length. An object whose height is 4 cm is placed 50 cm from a concave (diverging) lens. If the focal length of the lens is 30 cm, determine the characteristics of the image: Virtual Type (real or virtual): _______________ Location: _______________ Magnification: _______________ Height: _______________ 18.75 cm 0.375 (upright and smaller than object) 1.5 cm Click Click

31. Question-10 Negative sign indicates inversion. An object that is 5 cm high is placed 70 cm in front of a convex (converging) lens whose focal length is 20 cm. Determine the characteristics of the image: Real Type (real or virtual): _______________ Location: _______________ Magnification: _______________ Height: _______________ 28 cm -0.04 (inverted and smaller than object) 2 cm Click Click

32. Question-11 A lens produces the following optical effect. Which group of lens produces the above effect? A) Double concave B) Plano concave C) Double convex D) Plano convex Click Click

33. Question-12 Beams of light rays are traveling through air parallel to theprincipal axis of four different lenses. The light rays enterthe lenses and are refracted. In which diagram are the light rays correctly illustrated? Click Click

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