Focal Length of a Converging Lens

Proceedure: Set up apparatus as shown. For five different sizes of do, focus the image on the screen and measure di. (determine a suitable range for do) Pick lens with +5 or +10 printed on it (do not use the +15)

Observations: What is the number on printed on the lens _________

Obs
do
di
Characteristic of Image
size
attitude
type
1

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2

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3

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4

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5

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Calculations:

Obs
1/do
1/di
1/do + 1/di
f
1

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2

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3

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4

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5

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Average f

.

- Make a plot of do x di as a function of do + di and find the slope of the line.

Conclusion:

1.0 What is the focal length of the lens in meters?

Discussion:

2.0 What is the point of the graph and why should the slope yield the focal length?

3.0 Is the magnification of the lens constant for all observations?

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