LAB REPORT QUESTIONS 1. Including uncertainty, what value did you calculate for
ID: 1561749 • Letter: L
Question
LAB REPORT QUESTIONS
1. Including uncertainty, what value did you calculate for the focal length of the lens labeled as 10 cm? Did your value agree with the labeled value (10 cm)? Discuss any differences or causes or error between the two results. What was the average percent error between your measured and calculated magnifications? Would you say both values were close? Why or why not? Discuss what factors you believe led to any differences between the two magnification calculations.
2. For the double-lens image, what value did you calculate for the focal length of the lens labeled as 5 cm? How close was your value compared to the labeled focal length? What value did you calculate for the height of the final image and how closely did this match the height you measured? In each case (f and h) discuss any sources of error or uncertainty in your calculations.
3. Would you say that the lenses you used in this lab obey the lens equation? Why or why not? 4. Describe what you saw when you viewed the virtual image through the lens when you did part three. Did the size and position of the image match your expectations? (Be descriptive in your answer to this question; simple ‘yes’ or ‘no’ answers will not get you any grade.)
140 120 Average (om) Standard Dev lon) bol loml The virtual image looked down and 9.70 119 110 126 1:56 8 50 percent error 240 638 12 (cm) 4.794871795 110 ye do i 1 1.10 2.50 15 /13 SEExplanation / Answer
(1)
The average percentage error is = 6.37 %
Both values are not close 6.3 % is significance difference that need to be taken into consideration.
Error Analysis
One source of error in this experiment comes from uncertainties in positioning the lenses. The optical bench permits reasonably accurate positioning of lenses along the bench. However, the height at which the lenses are placed is not precisely adjustable. Also, the orientation of the lenses should be perpendicular to the optical bench and parallel to the lighted object. Adjustments in these directions are not available on the apparatus except by rough positioning of the lens inside the lens holder.
A second source of error in this experiment is due to aberrations in the lenses themselves. A full discussion of the deviations of physical glass lenses from the theoretical ideal is beyond the level of this course. However, it can easily be seen that the quality of images at the edges is quite different from image quality at the center. This suggests that the lenses used in this experiment have different properties at their edges than at their centers. One reason for this difference is that the lenses have different thicknesses at the edge and at the center. Many of the optics formulas used in this experiment assume that the lenses are thin to partly remove this difficulty.
Thirdly, there is the issue of determining when an image is properly in focus. When a real image is observed on a screen, there is a certain tolerance in the position of all instruments within which the image appears focused. This tolerance should be determined experimentally and included in your analysis. Finally, there is a huge systematic error in determining the magnification using the grid method in steps 7-9. You should independently determine how this error translates into your value for the magnification and what the possible ways of reducing it are
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