You might be able to use your cellphone screen as a light source if the room is totally dark. Assuming the focal length of the mirror is much smaller than the distance across the room, this will give you a fairly accurate measurement of the focal length. If you can't take the mirror out of the room, try to get a light source placed as far away from the mirror inside the room as possible. Finding the focal length of the mirror is critical to this issue, as without it you can't use any equations properly. The distance from the paper to the mirror is the focal length. Now see if you can adjust the distance between the paper and the mirror such that distant objects located outside the doorway are in focus on the paper. Hold the mirror such that you form an image of the doorway on a piece of paper held in a vertical plane parallel to the closed door. Good idea on the other method I will give that a try.Īnother experiment you can perform is to stand in a long hallway that has a glass doorway to the outside at one end. I think you would have to see this in person to be convinced. Any other distance and the image gets larger, less bright, and, by human eye, much less focused. The upper image, the blob of light on my makeshift projector-that is the best and sharpest the image could focus at. The object, the light bulb, the lower blob of light in the image, does not look this way in person it is a point-source light bulb as seen with the human eye. Neither the image or object are nearly as bright and spherical as what the camera captured above. A part number would be great.Īlso, what the camera and what the eye capture are very different. I had not considered the material of the projector screen detail before. I use what is available to me, but would certainly be excited to know that another kind projector screen would make this much easier. If I should use something different for a projector screen, by all means let me know. The screen in which to capture the light bulb image is white paper on the corkboard that's the top blob of light in the top image. I will check on Monday the focal lengths and see where I can get the object and image to appear at the same distance from the mirror. I'm not sure if this verifies the above statement or if the discrepancy is enough that this is what is not happening here. The image and object are pretty close together, 75 compared to 90 cm. "In other words, the image can be seen on a screen at the same location as the object if you place them at the center of curvature of the mirror." However, the magnification comes out to "1", that is, the image should neither have shrunk nor magnified with respect to the original object, and the image here is clearly well magnified. Yup, just verified it theoretically from the lens maker's equation. "You can form a real inverted image located at twice the focal length if you place the object at twice the focal length." I did that as carefully as I could and should be within a few centimeters. I measured the focal length crudely where the image flips from upside down beyond the focal length to where it switches to right side up, closer to the mirror within the focal length. When you say "twice the focal length", do you meant the center of curvature, C, of the mirror? Unless of course my focal length is 30-40 cm I'm pretty sure its not, less sure after this reply, though. Its hard to see from the images but I am pretty sure that the object is not at twice the focal length (100-120 cm). Now I am not sure if my typo is not the correct focal length. I thought the images above were a typo when I looked at them just now in putting 50 cm where I meant to write 60 cm. Pretty sure the focal length was 60 cm, I can check again. My question is: based on the lens maker’s equation, shouldn’t I see the image ONLY at q = 87 cm and at no other distance from the mirror? According to second semester ray diagrams, the ray lines do not converge at any other location except where the real image is supposed to form, and, not converging, it seems that no other image should be possible to be seen anywhere else. I measured the focal length crudely by moving the object back and forth and noting where it transitions from upside-down to right-side-up. The parameters are f = 60 cm, p = 200 cm, and q should be ~ 87 cm, as calculated from the standard lens makers equation in a second semester university of college physics course. I attached a series of images taken with a camera for a concave mirror, the Pasco SE-7573.ĭemonstration Mirror, Concave - SE-7573 - Products | PASCO Summary: Does the image distance q in the lens-maker's equation mean where real images form or where any image at all forms? If the former, what separates the real image from all other reflections?
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