you need
  • - lenses;
  • - light source;
  • - screen;
  • - line.
If you know the focal length of the lens, find its optical power by dividing the number 1 is the focal distance in meters.Focal length is the distance from the optical center to a point where all the refracted beams meet in one point.And for the collecting lens is a real value, and for the scattering - the imaginary (the point is based on extensions of the scattered rays).
In that case, if the focal length is unknown, then the converging lens can be measured.Secure the lens on a tripod, place it in front of the screen and send it to the back of the beam is parallel to the main opti
cal axis of the light rays.To move the lens until the screen light beams converges in one point.Measure the distance from the optical center of the lens to the screen - this will be the focus of a converging lens.Its optical power measure by the method described in the preceding paragraph.
When the focal length can not be measured, using a thin lens equation.To do this, between the screen and the subject (best fit hand-type light a candle or light bulb on a stand), set the lens.Move object and the lens so as to obtain an image on the screen.In the case of the diverging lens, it may be imaginary.Measure the distance from the optical center of the lens to the object and its image in meters.
Calculate the optical power of the lens:
1. Number 1 divide by the distance from the object to the optical center.
2. Number 1 divide by the distance from the image to the optical center.If the image is imaginary, before it put the sign "minus".
3. Find the sum of the numbers, get in claims 1 and 2, with signs in front of them.This will be the power of the lens.

optical power of the lens can have both positive and negative.