PHYSICS 106/1116

Lenses and Mirrors

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Introduction: Telescopes, microscopes, cameras, projectors, your eyes, all have one thing in common. What is it? We will talk about how these things work using the following.

Text Reference:  Haliday, Resnick, Walker 34.7

I. Ray tracing in converging and diverging lenses
  1. This will be done as a lecture-demo at the start of lab.

II. Converging Lenses
  1. Place the light source, a converging lens, and the screen in holders along the optical bench. Fix the position of the source and lens, and then adjust the position of the screen until a sharply defined image is formed on it.
  2. Determine the focal length of the lens experimentally. Compare it to the focal length calculated from the lens power (if given).
  3. Determine the magnification of the object (hint: there are two ways).


III. Concave Mirror

Repeat measurements, similar to those in part I, for the concave mirror.

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IV. Diverging Lens

Since negative or diverging lenses do not form REAL images of REAL objects, use the thin converging lens to set up a VIRTUAL OBJECT for the diverging lens. Your setup should be as shown below.  You will use this set up to determine the focal length of the diverging lens.  Remember, the image created by the converging lens is the object for the diverging lens.

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(1) source position
(2) convex/converging lens position
(3) screen position without lens 2
(4) concave/diverging lens position
(5) screen position with lens 2
(6) source distance: p2
(7) image distance: q2
(8) f2 (from lens formula)
(9) f2 (from 1 / P2)
(10) compare (8) and (9)

V. Convex Mirror

Determine the focal length of the convex mirror by using it in conjunction with the thin converging lens. First obtain a REAL image of the source using the lens alone. Interpose the mirror between the lens and the original image. Next, turn the screen around and move it between the lens and the mirror. Adjust the heights of the source, lens, and screen so the top of the screen covers the lower half of the lens and the REAL image can be seen on the screen. Move the screen and/or mirror to observe a sharp image on the screen. Record the data and calculations as before.

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(1) virtual object position
(2) mirror position
(3) final screen position
(4) source distance p
(5)image distance q
(6) f (from mirror formula)

V. Simulations: You can simulate some thin lens setups here: Optics Bench Applet

Write-Up

  1. If this is a formal lab (as indicated on the lab syllabus), you have been instructed as to whether this is an individual or group write-up, or an oral presentation. If it is a write-up, each person must submit the lab electronically as a word-processed document in Moodle before the next lab meeting. If it is a group write-up, you should all be submitting the same document. For written formal labs, remember to check the "write-up hints" page to be sure everything is included and check your write-up against the grading rubric.
  2. If this is an informal lab, work on the results together in your groups, and be sure to have your complete informal lab in your lab notebook and checked by the instructor before you leave.
  3. Remember to read the next lab and do the pre-lab before you come to lab next week! You may work on the pre-lab with others, but each person must submit her or his own work.

Department of Physics
Randolph College