Experiment 9: Lenses

Purpose: To observe characteristics of a converging lens and the image it produces from a light source

Materials:

• light source with arrow image
• large converging lens
• lens holder
• meter stick
• marker board
• optics bench

Set up:

Experiment:
1. First we determined the focal length of the lens by using the sun rays outside

f = 5.3

2. Then we took data by changing the distance of the lens from the light source by a factor of the focal length.

Object distance do, cm	Image distance di, cm	Object  height ho,  cm	Image       height    hi, cm	M	Type of      image
5 f = 26.5	7	8.8	2.3	0.26	inverted
4 f = 21.2	7.7	8.8	2.9	0.33	inverted
3 f = 15.9	8.4	8.8	4.6	0.52	inverted
2 f = 10.6	11.5	8.8	9.1	0.96	inverted
1.5 f = 7.95	15.95	8.8	n /a	1.8	inverted

3. Change the object distance to 0.5 f. What happens to the image?
 The image is found inside the lens and is no longer inverted.

If you cannot get an image on the card, take the card away and look through the lens at the object to view the image.  How would you describe the image?  Look through the lens at the object and view the image. How would you describe the image? 

The image is projected as it is seen from the slide of the light source.

4. Plot a graph of image distance, d_i, vs. object distance, d_o using centimeters.

5. Plot a graph of inverse image distance vs. negative inverse object distance.




slope = 0.9037
y-intercept = 0.1748 which represents the minimum image distance the lens will produce.

9.         Using the regression line from your graph and substituting in the axis values, write the equation that relates d_i and d_o below.

Summary: From this experiment we have successfully proved the equation that relates focal length to the object and image distance. p is positive when the object is on the incoming light ray side. q is positive when the image is on the outgoing light ray side.