#9 Lenses:

Objective: 

       This experiment is designed to investigate some characteristics of converging lens.

Procedures:

1.      Determine the focal length of the lens. The focal length is 20 cm

2.       Place the lens in the holder, and place the filament on one side of the lens. The distance between the lens and filament is set in different values as 5, 4, 3, 2, 1.5 focal length.

3.       Place the whiteboard at the other side and find the clear image if applicable. Record the distance to the lens.

4.       Reverse the lens to see if the direction would affect the lens’s optical property.

Results:

Recorded values as shown:

Object Distance /cm	Image Distance /cm	Image Height /cm	Magnification	Type of image		Object height
100	24	2.5	0.284	Real and inverted		8.8 cm
80	25	3.5	0.398	Real and inverted		Focal length
60	28	4.5	0.511	Real and inverted		20 cm
40	37	8.5	0.966	Real and inverted
30	50	14.5	1.647	Real and inverted
10	\	\	\	Virtual and same

The image distance with respect to 10 cm object distance is immeasurable, by observation, the image is in the same side as the object and the height is about half of the object and 5 cm to the lens.

Discussion:

       By reversing the lens, the image did not change, so reserving the lens does not affect the optical property of the lens. By covering half of the lens, the image became much dimmer, but still kept the same image height and type; thus, covering the lens does not affect the type of image.

       The virtual image formed by 10 cm object lens is shown as:

       Which is verified by observation.

       The measured distance satisfy the lens as 1/d_o + 1/d_i =1/f

      

Object distance/cm	100	80	60	40	30		1/f
1/d0 + 1/di	0.052	0.053	0.052	0.052	0.053		0.050
Percent difference	3.333	5.000	4.762	4.054	6.667

The error may caused by human error in finding the clearest image and the focal length of lens which may not be 20 cm as marked.