Go to the PhET website and run the geometrics optics simulation http://phet.colo

Question

Go to the PhET website and run the geometrics optics simulation http://phet.colorado.edu/sims/geometric-optics/geometric-optics_en.html

1. The following settings are to be used throughout Part 2 of this experiment: Principal Rays – On Virtual Image – On Screen – On Ruler – On Lens Diameter – 0.8 m

2. Set the Focal Length to 20 cm on the Ruler. This can be done by using the Curvature Radius and the Refractive Index sliders. Many different combinations will give the same Focal Length. It doesn’t matter which combination is used. Whichever one you use, record the values at the top of Table 2 for 20 cm.

3. Next, set the Object Distance to 10 cm; this is the first Object Distance in Table 2. This is done by aligning the right end of the Ruler against the lens centerline and then moving the SourcePoint to a position 10 cm to the left of the lens centerline. The Object Distance should be measured along the upper Principal Ray.

4. Measure the Image Distance by aligning the left end of the Ruler against the lens centerline and then measuring along the lower Principal Ray to the point of intersection of all the Principal Rays. Record this Distance.

5. Repeat Steps 3 and 4 for the remaining Object Distances of 20, 30, 40, 50, 60, 70, and 80 cm; these are the remaining Object Distances in Table 2. Record all the Image Distances.

6. Now, repeat Steps 2, 3, 4, and 5 for the remaining Focal Lengths of 30, 40, 60, 80, and 100 cm; these are the 5 remaining Focal Lengths to be studied. Their Data will be recorded in Tables 3, 4, 5, 6, and 7.

7. Once data collection has been completed for Part 2, the analysis of the data can begin. Measured Image Distances have been collected. These will now be compared with the Image Distances predicted by theory. In Tables 2 – 7, the 3rd column will receive the entries for the Theoretical Image Distances. Using FL as the Focal Length and OD as the Object Distance and the Lensmaker formula, we compute the Image Distance (ID) as: (ID=(FLOD))((OD-FL) ) Compute and enter all of these values into the Theoretical Image Distance columns in Tables 2 – 7.

8. The Percentage Error of the measurements relative to theory will now be computed by using the following formula: "% Error =((Measured - Theoretical)/Theoretical) * 100%" The Percentages, rounded to one decimal place, are to be entered in the appropriate cells of Column 4 in each of the Tables.

Explanation / Answer

Focal Length of the lens, f = 20cm

Object distance, u = - 10cm, Negative sign indicates that the object is to the left of the lens

Image distance, v is obtained using the Lens Formula.

Lens Formula : 1/u + 1/f = 1/v

-> 1/v = 1/u + 1/f = 1/20 + 1/(-10) = 1/20-1/10 = -1/20 = 1/(-20) cm

4)hence, Image distance is given by v = -20cm

Similarly, Using the above formula of 1/u + 1/f = 1/v, we can put in the values of u and f as given is (5) and (6) and obtain the desired Image distance v using this formula.

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