Physics Lab: Images formed by a Converging Lens
Cherno Okafor
Mr. Ebrahimi
SPH4U7
December 28th, 2012
Data Collection and Processing
Initially, I held a converging lens in a dark part of the room allowing light from a distant object to pass through it and onto the screen. I kept moving the screen back and forth until the image was clearly focused. Hence, I found my focal point by measuring the distance between the lens and the screen, which was f =19cm.
Based on my data collection, in all the cases where the image type was real the image attitude was inverted, and when the image attitude was upright the image type was virtual (Beyond f). I also noticed a relation between di and do. That is, the shorter the do was, the longer the di was.
I will now summarize the four laws of reflection for forming images by a converging mirror.
- Any ray travelling parallel to the principal axis will reflect through the principal focal point.
- Any ray travelling through the principal focal point will reflect parallel to the principal axis.
- Any ray travelling through 2F will reflect back along itself.
- Any ray striking the vertex of the mirror will reflect so that angle of reflection equals the angle of incidence.
There are 6 cases which to consider for this lab. I will explain in detail each case and the implications on the results of the chart.
Case 1: The pin object is located beyond the 2f point (between infinity and 2f):
When the object is located at a location beyond the 2f point, the image will always be located somewhere in between the 2f point and the focal point f on the opposite side of the lens. In this case, the image will be an inverted image. If the object is upright, then the image will be upside down. Using the screen at the image location, the inverted image can be projected. The image is also real and smaller; with a magnification value of less than 1.
Case 2: The pin object is located at 2f:
When the object is located at the 2f point, the image will also be located at the 2f point on the other side of the lens. In this case, the image will be inverted. The image dimensions are equal to the object dimensions. Thus, the absolute value of magnification is exactly 1. The image is again real and can be projected onto the screen at the image location.
Case 3: The pin object is located between 2f and f:
When the object is located in front of the 2f point, the image will be located beyond the 2f point on the other side of the lens. In this case, the image will be inverted while the object is upright. The image would be larger than the object and the absolute value of the magnification would be greater than 1. Finally, the image is a real image and the image can be projected onto the screen at the image location.
Case 4: The pin object is located at f:
When the object is located at the focal point, in this case at 19cm from the lens, no image is formed. Finally, this image will be located at infinity. The refracted rays neither converge nor diverge; they travel in a parallel direction to each other and hence cannot intersect and produce an image as shown in the diagram below.
Case 5: The pin object is located in front of f:
When the object is located in front of the focal point, the image will always be located somewhere on the same side of the lens as the object. The image is located behind the object in this case and the image will be upright. If the object is upright, the image will be upright and vice versa. The image is also larger than the object and the absolute value of magnification is greater than 1. Finally, a virtual image is formed. Light rays diverge upon refraction; for this reason, the image location can only be found by extending the refracted rays backwards on the object’s side of the lens. Any attempt to project this virtual image upon a sheet of paper would fail since light does not actually pass through the image location.
Case 6: The pin object is at infinity:
When the object is located at infinity, one can project its image on a screen held infinity units away. The image will be real, however the attitude will be indeterminate and the size will be infinitely small. Finally, this image position will be at the real focal point.
Conclusion/Evaluation:
There is an evident relationship between the object distance and object size and the image distance and image size. Starting from a large value, as the object distance decreases (moves closer to the lens), the image distance increases; meanwhile, the image height increases. At the 2f point, the object distance equals the image distance and the object height equals the image height. As the object distance approaches one focal length, the image distance and image height approaches infinity. Finally, when the object distance is equal to exactly one focal length, there is no image. In addition, by altering the object distance to values less than one focal length, the object produces images that are upright, virtual, and located on the same side of the lens as the object. Finally, if the object distance approaches 0, the image distance approaches 0 and the image height ultimately becomes equal to the object height. These patterns are depicted in the diagrams.
Error Analysis:
One error that could occur during this lab is inaccurately measuring the Image Distance. This would result in incorrect observation results. Another error that could occur is not measuring the screen image’s image distance at a location that does not exactly focus the image. This would result in an incorrect reading for the distance of image.
by
cherno (student)
