1. Ying Yi PhD Lab 5: Lenses 1 PHYS II lab @ HCC

2. Outline PHYS II lab @ HCC 2 Basic concepts: image, convex lens, concave lens, focal length Lab objectives Lab procedure (experiment I, II, III) Questions

3. Images 3 How formed? Images are formed at the points where rays of light actually intersect or where they appear to originate. Images can be formed by refraction (thin lenses) and reflection (mirror). Types: Real image and virtual images Magnification: PHYS II lab @ HCC Basic concepts

4. Flat mirror 4 How formed? Type of image? Magnification? Reflection Virtual PHYS II lab @ HCC

5. Converging lenses 5 They have positive focal lengths. They are thickest in the center PHYS II lab @ HCC Diverging lenses They have negative focal lengths. They are thickest at the edges.

6. Focal Length of Lenses The focal length, ƒ, is the image distance that corresponds to an infinite object distance. A thin lens has two focal points, corresponding to parallel rays from the left and from the right. 6 PHYS II lab @ HCC

7. 7 Focal Length of a Converging Lens The parallel rays pass through the lens and converge at the focal point. The parallel rays can come from the left or right of the lens.

8. PHYS II lab @ HCC 8 Focal Length of a Diverging Lens The parallel rays diverge after passing through the diverging lens. The focal point is the point where the rays appear to have originated.

9. PHYS II lab @ HCC 9 Lens Equations The geometric derivation of the equations is very similar to that of mirrors.

10. Lens Equations and Signs The equations can be used for both converging and diverging lenses. A converging lens has a positive focal length. A diverging lens has a negative focal length. 10 PHYS II lab @ HCC

11. Sign Conventions, Table 11 PHYS II lab @ HCC

12. Ray Diagrams for Thin Lenses Ray diagrams are essential for understanding the overall image formation. Three rays are drawn. The first ray is drawn parallel to the first principle axis and then passes through (or appears to come from) one of the focal lengths. The second ray is drawn through the center of the lens and continues in a straight line. The third ray is drawn from the other focal point and emerges from the lens parallel to the principle axis. There are an infinite number of rays, these are convenient 12 PHYS II lab @ HCC

13. 13 Note the changes in the image as the object moves through the focal point. Ray Diagram Examples

14. Combinations of Thin Lenses The image produced by the first lens is calculated as though the second lens were not present. The light then approaches the second lens as if it had come from the image of the first lens. The image formed by the first lens is treated as the object for the second lens. The image formed by the second lens is the final image of the system. 14 PHYS II lab @ HCC

15. Combination of Thin Lenses, 2 If the image formed by the first lens lies on the back side of the second lens, then the image is treated at a virtual object for the second lens. p will be negative The overall magnification is the product of the magnification of the separate lenses. It is also possible to combine thin lenses and mirrors. 15 PHYS II lab @ HCC

16. Combination of Thin Lenses, Example 16 PHYS II lab @ HCC

17. Objectives PHYS II lab @ HCC 17 Measure focal lengths of convex lenses Image formation by combination lenses

18. Equipment PHYS II lab @ HCC 18 Optical bench, Pasco Optics set (illuminated object; screen; diffuser; two converging lenses, +127 mm, +18 mm; diverging lens, -22 mm; lens holder), light source, ruler with millimeter scale.

19. PHYS II lab @ HCC 19 Convex Lens (127 mm)Experiment I Object distanceImage distanceFocal lengthObject heightImage height

20. PHYS II lab @ HCC 20 Convex Lens (18 mm) Experiment II Object distanceImage distanceFocal lengthObject heightImage height

21. Combination of Lenses (III)

22. Reference image: Light Souce-Object-Lens-Image

23. Close Up – See the Distance Mark

24. Questions 24 1. A converging lens of focal length 10.0 cm forms images of an object situated at various distances. (a) If the object is placed 30.0 cm from the lens, locate the image, state whether it is real or virtual, and find its magnification. (b) Repeat the problem when the object is at 10.0 cm and (c) again when the object is 5.00 cm from the lens. 2. Solve problem 1 for diverging lens. 3. Two converging lenses are placed 20.0 cm apart, with an object 30.0 cm in front of lens 1 on the left. (a) If lens 1 has a focal length of 10.0 cm, locate the image formed by this lens and determine its magnification. (b) If lens 2 on the right has a focal length of 20.0 cm, locate the final image formed and find the total magnification of the system. 4. What are telescope and microscope? How can you apply this knowledge to produce them? PHYS II lab @ HCC