LENS LAB

Convex Lens Image

Step 1. Assemble the equipment as shown by your instructor. For this first part all you need is the thin convex lens and the screen.

Point the optical bench toward an open doorway through which light is coming. Move the lens back and forth until a clear image of a distant object is formed on the screen.

Q1. Describe the characteristics of the image fully.

Now look, with your eye, at the same object.

Q2. Compare the object with the image on the screen.

Convex Lens Focal Length

Step 2. Place the light source on the end of the optical bench so the point source points through the lens to the screen. Place the thin convex lens 1/2 way down the bench. The screen should be on the opposite side of the lens from the light. Adjust the screen until you obtain the smallest, sharpest dot on the screen. The distance between the screen and the lens is the focal length of the lens. Turn the lens around and repeat measurement.

f1 = ________, f2 = __________ or no focus found (if no focus found put x's on spaces and circle no focus found)

Step 3. Repeat with the thick convex lens

f1 = ________, f2 = __________ or no focus found (if no focus found put x's on spaces and circle no focus found)

Step 4. Repeat with the concave lens.

f1 = ________, f2 = __________ or no focus found (if no focus found put x's on spaces and circle no focus found)

Q3. How does the reverse focal length compare with the front focal length?

Q4. Which lens wouldn't allow you to find a focus? Why?

Q5. Compare the physical shape of the two lenses you did find a focus for and relate this to the focal length.

Step 5. Now that you know the focal length of the lens, change the light source to the arrows. It should still be at the end of the bench. Place the thick lens at a distance of 4 f ( 4 x the focal length) from the light. Move the screen along the bench until a clear image is formed. Record the Object Distance (distance of light from lens), Image Distance (distance of screen from lens), Object size (length of light arrows from top to bottom), and Image size (length of light from lement to top of light on screen). Repeat this procedure with the arrow slit at 3f, 2f, (11/2)f, f, and f/2. Fill in table. Don't forget to write in what "f" is in the top left corner.
 

Q7. On the basis of your data, describe qualitatively what happens to the position and size of the image when the object is moved toward the lens.

Q8. Where did the image disapear? Why?

Q9. Examine your data table carefully. What general relationships do you see?

Step 6. Calculate the following and fill in the table.