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# Experiment to Find the Focal Length and Power of a Diverging Lens.

Extracts from this document...

Introduction

Joanne Bell

Experiment to Find the Focal Length and Power of a Diverging Lens

Aim

The aim of this experiment is to measure the focal length and power of a diverging lens. Since negative or diverging lenses do not form real images of real objects, an experimental virtual object will need to be set up for the diverging lens by using a converging lens. To do this, place a converging lens in front of the diverging lens. If the converging lens has a shorter focal length than the diverging lens, the two-lens combination will form a real image of a distant object.

Figure 1

When the lenses of individual focal lengths f c and f D, are placed in contact, the effective focal length f of the combination is given by:

Equation 1

Middle

Set up the apparatus as shown in figure 2 but with both the converging and diverging lenses in the lens holder. With the object to lens distance, u, at 6f , move the viewing screen until a clearly focused image can be seen.Measure the image to lens distance and include uncertainty measurements (where the distance can be changed more but the image is still in focus).Repeat procedures 2 and 3 for object to lens distance at 5f, 4f, 3f, 2f, and just over 1f.Solve the lens equation (Equation 1) using the values found in the above procedures to give a more accurate combined focal length.Use Equation 2 to find the power of the combined lens.

Step 3: Finding the focal length and power of the diverging lens:

Conclusion

/p>

50

11

0.02

0.090909

0.110909

9.016393

60

12.4

0.016667

0.080645

0.097312

10.27624

Diverging lens:

 u, object to lens (cm) v, image to lens (cm) 1/u 1/v 1/f f (cm) 15 170 0.066667 0.005882 0.072549 13.78378 30 31 0.033333 0.032258 0.065591 15.2459 45 22 0.022222 0.045455 0.067677 14.77612 60 17 0.016667 0.058824 0.07549 13.24675 75 16 0.013333 0.0625 0.075833 13.18681 90 15 0.011111 0.066667 0.077778 12.85714

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