PhysicsLAB Lab
Student Lens Lab

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  • one converging lens
  • one sheet of white paper attached to cardboard
  • three-four meter sticks
Outside, one lab partner, "the object" should stand in the sunshine approximately 12-15 meters in front of the lens. The partner holding the lens and screen should stand in the shade and move the paper screen to the correct position to get as sharp as image as possible. The third member needs to measure the distances from the object to the lens and the distance of the paper screen from the back of the lens as carefully as possible and record them in the data chart for Trial #1.
Repeat by relocating your lab partner's to a new position approximately half as far from the lens, 6-8 meters away. Again, adjust the position of the screen, measure both do and di carefully and record them both in the data chart for Trial #2.
Finally, use the lens to focus the sun's rays to as tight a "point image" as possible on a concrete wall or a sidewalk. Be careful to not STARE at the image - it will be very bright! Record the distance between the lens and the concrete as di for an object located at infinity, the sun, for Trial #3.

Using your data from each trial and the thin lens equation, solve for the focal length of your lens. Show all of your calculations on the back of this paper, or on an attached sheet of notebook paper.
Trial (cm) (cm) (cm)
What was the average focal length (in cm) for your lens? 

Which two trials were in closest agreement?
Why do you think these two trials were closer to each other than to the other trial? 

What recommendation would you make to improve the precision of this lab? 

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