Converging+Lenses

Converging Lenses

Objective: The purpose of this lab was to figure out what the focus of a converging lens through the use of the thin-lens equation and a diagram.

Apparatus:
 * Computer
 * Phet Online Simulation

Procedure:
 * 1) Open Phet by the following hyperlink: http://phet.colorado.edu/sims/geometric-optics/geometric-optics_en.html
 * 2) First change "marginal rays" to "principal rays" in the top left corner of the screen.
 * 3) Drag the pencil up until the bottom of the eraser touches the principal axis.
 * 4) In the setting up of the simulation lab, change the pencil distance from the lens to your liking.
 * 5) Click the Ruler button in the top right corner of the screen. This will enable you to measure the object distance and the image distance.
 * 6) Put the data into the thin-lens equation, which will enable you to find the focus.
 * 7) Measure the actual focus and compare with the results of the equation.
 * 8) Use this data to find the percent difference. Average your percent differences.
 * 9) Repeat steps 4-8 changing the curvature radius but keeping the reflective index of glass (1.53) the same.
 * 10) Note: feel free to change the curvature radius, refractive index, or diameter.

Analysis Questions: What is the only thing that could cause a percent difference? Does the thin-lens equation accurately represent the relationship between the focus, object distance, and image distance? Was the image upright or inverted, larger or smaller, real or virtual? What did you notice when you changed the curvature radius, refractive index, or diameter?

No graphical analysis is required for this lab beecuase neither the knowledge of the area nor the slope is needed in this experiment.

Tutorial: media type="file" key="Converging_Lense_lab_Tutorial_Video.swf" width="481" height="401" align="center"

**Sample Trial**
1) 1/Do + 1/Di = 1/f; curvature radius = .8 m Do = 140 cm Di = 161 cm 1/140 + 1/161 = 1/f 43/3220 = 74.88 cm actual focus = 76 cm

2) 1/Do + 1/Di = 1/f; curvature radius = .46 m Do = 145 cm Di = 62 cm 1/145 + 1/62 = 1/f 1/f = 51/2201 f = 43.16 cm actual focus = 43 cm

__Percent Difference__

1) (76 - 74.88) / 76 x 100 = 1.47%

2) (43.16 - 43) / 43.16 x 100 = .37%

Average = (1.47 + .37) / 2 = .92%