PHY13L - E403 - Refraction from a Spherical Surface - Thin Lens

ANALYSIS OF DATA / REMARKS

For the entire experiment, we experimentally deter-mined the focal lengths of two lenses with an actual focal lengths of 10cm and 20cm respectively.

For the Part A of the experiment, focal length is determined using an infinity object. In this case, our best infinity object is the view of the sky from the laboratory room's window. Values shown are exact from the actual value which gives us no percentage error for both lenses. Focal length is computed using the lens equation where the image distance is approaching infinity which leads is to an equation where focal length is equal to the image distance.

Part B of the experiment uses a finite object where in this case is an image projected by the light source provided. In this part of the experiment, the screen and the light source is a meter apart from each other and the lens is somewhere in between. Lens is moved back and forth until the image formed on the screen is sharp. There would be two position of the lens where image formed is sharp where our data shows that these positions are interchangeable and are conjugate. This applies for both lenses with 10cm and 20cm focal lengths respectively. Focal length in this case is also obtained using the lens equation.

Using graphical method, we can also determine the focal length of the lens like what we did on the Part C of the experiment. In this part of the experiment, we used the 10cm-focal length lens. Distance between the screen and the light source is changed for every trial from 110cm to 90cm to 85cm apart respectively. Percentage difference is also computed where it shows that percentage difference is greater on the second position where lens is closer to the screen this is because the image height is very small and is hard to measure accurate using a ruler measuring millimeters.

Common possible source of errors for this experiment is measuring. Small difference on distance may show huge effect on the data.

 

CONCLUSION

We were able to determine the focal length of the lens using different location of the object including an infinity object and we were able to understand, with the help or out instructor, the graphical method in getting the focal length of a lens.

Refraction is the blending of light ray as it hits a material of different optical density. Transparent materials like lenses can refract parallel ray of light and can produce an image. Convex lens is used on our experiment which has middle-part thicker. Focal length's relation to the object and the image is given by the thin lens equation where focal length is the difference on product and sum of the object and image distance from the lens. . There are two positions of the lens where image formed is sharp, these positions are interchangeable and are conjugate. The magnification of the lens is the ratio of the image height and the object height, and is also related to the distances of the object and image from the lens.

Lenses play a very important role on the discovery of various things we know today.  Telescope and microscope uses lens to magnify things from afar or a very small particle. Without these lenses, such things would not be possible. This experiment helped me understand how light rays behave on thin lenses and focal points differences plays its part.