4/1 Lenses

Purpose

     The purpose of this experiment was to observe characteristics of a converging lens when the object is placed on one side of the lens and the real inverted image is placed on the other side of the lens.

Experiment

 

Measuring the focal length: 5.0 ± 0.5 cm

 

 

Set up

 

Data and Analysis

 

d0(cm)	di±0.2(cm)	h0±0.2(cm)	hi±0.2(cm)	Md	Mh	Type of image
5f=25±2.5	7.4	8.8	2.3	0.296±0.042	0.261±0.030	inverted and real
4f=20±2.0	8.4	8.8	3.4	0.42±0.058	0.386±0.033	inverted and real
3f=15±1.5	8.9	4	2.6	0.593±0.081	0.65±0.087	inverted and real
2f=10±1.0	11.8	4	4.5	1.18±0.153	1.125±0.112	inverted and real
1.5f=7.5±0.75	18.3	1.1	2.8	2.44±0.301	2.545±0.789	inverted and real

 

When object distance is 0.5f, the light rays could not form image on white board (virtual image). If look through the lens, we observed a bigger and upright image.

 

 



 

1/q = -1/p + 1/f

1/q = -m/p + b

so, m should be 1 and b should be 1/f (0.2 ± 0.02 cm^-1)

However, the experimental m= 0.82 and experimental b= 0.165.

% difference of m= (1-0.82)/1 X 100% = 18%

% difference of b = (0.2-0.165)/0.2 X 100% = 17.5% ± 7.5%

 

Conclusion

     According to table 1 and graph 1, as the object distance decreased, the image distance increased. Therefore, the image and object distance had inverse relationship as shown in graph 1. Also, the images formed from a converging lens is always real and inverted. When half of the lens was covered, the image became dimmer since the light passed through the lens was decreased by a factor of 2. Besides, as the object distance became closer to the lens, the image size and distance became larger. At 0.5f, there was no image because the image was between the vertex and the focus; hence, the image became virtual.

      The experimental m was 0.82, with a percent error of 18%; percent difference of b (1/f) was 17.5% ± 7.5%. Therefore, the percent difference of b lies within a range of 10-20%, and 10% was within the allowable range. The 20% difference could be the focus was not as accurate as it should have been. Unclear images at small object distances also contributed to this error. This was because the image became dimmer and unclearer as the object distance decreased. Hence, uncertainty became greater since it became harder to see the actual height of the image.