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Understanding Convex Lens Characteristics & Image Formation

Learn about how convex lenses converge light rays and form images in different scenarios. Practice calculations and lens applications.

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Understanding Convex Lens Characteristics & Image Formation

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  1. Physics Review Lenses

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

  3. Lenses 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

  4. 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

  5. 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

  6. 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

  7. 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

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

  9. 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

  10. PRACTICE

  11. The negative sign indicates inversion. 14.1 Lenses Slide: An object whose height is 0.10 m is placed 1.0 m from thefocal pointof a converging lens whose focal length is 0.50 m. Determine the height of the image. Given Calculation of object distance Calculation of image distance Click

  12. A B C D 14.2 Lenses Slide: Which of the following lenses correctsthe eye defect known as myopia? Click

  13. Nearsightedness 14.3 Lenses Slide: Which type of lens is used to correct hyperopia? Thicker in the middle than at the ends. A) Plane B) Plano-concave C) Concavo-convex D) Convex-concave Myopia (farsightedness) is corrected with a Concavo-concave lens. Thicker at the ends than in the middle. Click

  14. Answer 14.4 Lenses Slide: Click

  15. This ray should go thru V since it is refracted without being bent. This ray should go thru F since it emerges parallel to the principal axis. parallel refracted ray This ray should go thru F since it arrives parallel to the principal axis. parallel incident ray 14.5 Lenses Slide: Click

  16. 14.6 Lenses Slide: An object that is 4.0 cm tall is placed 7.0 cm from a converginglens that has a focal length of 2.0 cm. Calculate the height of the image formed by this lens. The negative signindicates inversionand may be ignored. Answer The image is 1.6 cm tall. Click

  17. 14.7 Lenses Slide: As illustrated below, an object is placed infront of a diverging lens. Image Which of the following statements correctly describes thecharacteristics of the image formed. A) Virtual, upright, smaller and on the same side as the object B) Real, upright, smaller and on the same side as the object C) Virtual, inverted, larger and on the opposide side of the object D) Real, inverted, larger and on the opposide side of the object Click

  18. Center of lens, V Answer 14.8 Lenses Slide: F V F’ Converging lens Draw a ray connecting the object to the image in order to establish the center of the lens, V. Click

  19. 14.9 Lenses Slide: Karen wants to draw a mural of her dog on a wall. Using a projectorshe displays a picture of her dog on the wall. The focal length of theprojector lens is 35 mm. She needs to position the projector so thatthe real image of the picture of the dog has a magnification of 40. How far from the wall must the projector lens be? Note that since the image is real, it is invertedand the magnification factor is negative. Answer

  20. 14.10 Lenses Slide: Construct a ray diagram to locate the image formed by the lensillustrated below. This is the symbol for a converging lens Top (object) point Bottom (image) point Image Bottom (object) point Top (image) point Click

  21. The End … and good luck!

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