The lens has optical power. It is measured in dioptries. This size shows increase in a lens, that is that, how strongly beams refract in it. Change of the sizes of objects on images, in turn, depends on it. Usually optical power of a lens is specified by her manufacturer. But if there is no similar information, then measure it independently.
It is required to you
- - lenses;
- - light source;
- - screen;
- - ruler.
Instruction
1. If the focal length of a lens is known, then find its optical power, having divided number 1 into this focal length in meters. The focal length is equal to distance from the optical center to the place in which all refracted beams gather in one point. And for the collecting lens it is value valid, and for disseminating - imaginary (the point is under construction on continuations of scattered beams).
2. In case the focal length is unknown, then for the collecting lens it can be measured. Strengthen a lens on a support, arrange before it the screen, and direct to it from a reverse side a bunch of light beams parallel to its main optical axis. Move a lens until light beams does not agree on the screen in one point. Measure distance from the optical center of a lens to the screen - it is and there will be focus of the collecting lens. Measure its optical power by the technique stated in the previous paragraph.
3. When it is impossible to measure focal length, use the equation of a thin lens. For this purpose between the screen and a subject (the light candle arrow or bulbs on a support best of all will approach) establish a lens. Move a subject and a lens so that on the screen to receive the image. In a case with the disseminating lens it can be imaginary. Measure distance from the optical center of a lens to a subject and its image in meters.
4. Calculate the optical power of a lens: 1. Number 1 divide into distance from a subject to the optical center.2. Divide number 1 into distance from the image to the optical center. If the image imaginary, before it put sign "minus".3. Find the sum of the numbers which turned out in subparagraphs 1 and 2 taking into account signs before them. It will also be the optical power of a lens. The optical power of a lens can have both positive, and negative value.