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Lab 2: Light and Lenses

Tyler Junior College. Lab 2: Light and Lenses. Department of Physics and Astronomy. Physics 1403 Stars, Galaxies and The Universe. The Lab. The purpose of this lab to see how light passes through lens as the light travels through the telescope.

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Lab 2: Light and Lenses

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  1. Tyler Junior College Lab 2: Light and Lenses Department of Physics and Astronomy Physics 1403 Stars, Galaxies and The Universe

  2. The Lab • The purpose of this lab to see how light passes through lens as the light travels through the telescope. • We will see that the simple refraction telescope is designed around the focal lengths of the objective lens and the eye piece lens. • We will look at the real images that are formed in a telescope and that they can be inverted, erect, and reverse, thou not correctly oriented.

  3. Shapes of Lenses

  4. Types of LensShape determines Function • Function-Converging (Positive)-to a point –Image Diverging (Negative)-away-No Image • Shape-Convex-Converging Narrow at the top and bottom and wider in the middle. (Double or bi-Convex Lens) Concave-Diverging Narrow in the middle and wider at the top and bottom. (Double or Bi-Concave Lens)

  5. Converging Lens d- thickness f-focal length D-diameter or Aperture D

  6. Diverging Lens

  7. The Lens -Refraction • Curved surface glass bents incoming light due to decrease in speed of light moving into a denser medium toward a point called a focal point where an image is formed. • There will be more on Lenses and Telescopes in Lab 2.

  8. Simple Refracting Telescope

  9. The Lab Task • This lab is in three main parts: • First, determine the diameter (D), thickness (d), local length (f), the F numbers (Fn) and the size, orientation and brightness of the image formed by each lens. PART 1 • Second, determine the focal length of each lens by examining the distances between the object viewed and the image formed, along with more on the size, orientation and brightness. PART 2 • Third, design a simple refractor telescope, determine the lenses needed and relationship of each lens’s focal length in the telescope

  10. First Things First • Preliminary to doing the lab, we will: NOTE: Care should be used with the lens. • Try not to scratch, chip or break them. • It may be necessary to clean the lenses first. • Hold them by the edge only. • Place them on the paper towel or lens cloth when no in use. • First, place a very small piece of scotch tape on the edge of each lens and number them 1-4. • Second, measure the diameter (Aperture or D) and the thickness (d) of the four lenses. We will use a measuring device that measures small items, called a Vernier Caliper. Record this information in PART 1 DATA TABLE.

  11. The Math • 1 in. (inch) = 25.4 mm (millimeters) “1/1000 meter”[0.001 m] • 10 mm = 1 cm (centimeters) “1/100 meter” [0.01 m] • 1 m (meter) = 100 cm = 1000 mm • 1m = 39.37 in.

  12. Therefore … • Change in. to mm: X in. by 25.4 • Change mm to inches: ÷ mm by 25.4 • Change cm to mm: X cm by 10 • Change mm to cm: ÷ mm by 10 • Change m to mm: X m by 1000 • Change m to cm: X m by 100 • Change mm to m : ÷ mm by 1000 • Change cm to m: ÷ cm by 100 • Change m to in. : X m by 39.37 • Change in. to m: ÷ in. by 39.37

  13. Measure Diameter in cmwith the Vernier Caliper

  14. Aperture (Diameter) of Lens 5 cm 5.0 cm + 0.07 cm =5.07 cm

  15. Measure thickness in cm

  16. Thickness of Lens 0 cm 1 cm “0.5 cm” =0.58 cm + “0.08 cm”

  17. PART I Setup Bright Light Lens in Lens Holder Screen and Screen Holder cm meter stick Optical Bench Accessory Supports

  18. Support cm meter stick Measurement Mark Optical Bench 101.0 cm

  19. Align Screen and Lens

  20. Align Screen, Lens and Light to form Real Image Note: Size, Orientation (which side is the lamp holder on at the front of the room), Brightness of Real Image to Light Bulb from the same distance with you eye and…

  21. Location of Real Image 101.0 cm 94.8 cm Focal length (f) = 101.0 cm -94.8 cm = 6.2 cm

  22. Calculations • F Number (FN) • FN = f/D where f is the focal length and D is the Aperture (Diameter)

  23. PART II Orientation Light Note the direction of the arrow and the ball.

  24. PART II Setup do (Object Distance di (Image Distance)

  25. Real Image Orientation, Brightness, Size and…

  26. Location of Real Image 44.1 cm 50.0 cm f = 50.0 cm – 44.1 cm =5.9 cm

  27. Calculations • Focal Length (f ) • f = Where do is the distance (of the object) from lens to light and di is the distance (of the image) from the lens to the screen. (do)(di) do + di

  28. PART III Simple Telescope Bright Light Objective Lens Eye Piece Lens

  29. Objective and Eye Piece Lens Selections • See the Reading assignment or the lab instructions on how to determine which lens will be the objective and which will be the eye piece.

  30. Align Lenses and Light

  31. More Alignment!

  32. Looking Through Your Telescope Note Fuzzy Image!

  33. Focused Image After Moving Eye Piece Note the orientation: Erect, Inversed, Reversed or Correct?

  34. Distance Between Lenses?

  35. Calculation • Magnification (M) • M = • Where fo is the focal length of the objective lens (AND THE TELESCOPE) and fe is the focal length of the eye piece lens. fo fe

  36. Physics 1403 Lab 2 –Light and Lenses The End

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