**Theory:**

The lens equation:

gives the relation between the distance from the object to the lens, d_{o}, the distance from the image to the lens, d_{i}, and the focal length of the lens.

The focal length of a thin lens is given by:

,

where R_{1}is the front radius of curvature, R_{2}is the back radius of curvature.

Here, the equations are written according to the following convention:- Any distance to a real location is taken as positive
- Any distance to a virtual location is taken as negative
- The radius of curvature of a surface is positive if that surface is convex (the reality of the lens lies behind it)
- The radius of curvature of a surface is negative if that surface is concave (the imaginary region lies infront)

,

where f is in**meters**and P is in Diopters.**Initial settings:**- Select "Virtual Image" and "Ruler" from the options to the right.
- You can click on the "Change object" button to change the object, but it really doesn't matter.
- Set "curvature radius" to 0.65; "refractive indes" to 1.51, and diameter to "0.74" from the slidebars on the top.
- Select the "Principal Rays" radio button from the top left.

**Activity 1: Determine the focal distance of and the image produced by a thin lens.**- Additional Settings:
- Perform the experiment:
- Drag the object on the left to a distance 140 cm from the front of the lens.
- Measure where the image is located. Write down the orientation and the type of image, that is, upright/inverted and real/virtual.
- Repeat the procedure for 3 other distances. The values are given in the data table below.

- In your lab notebook, write down the data in the following format:

d _{o}(cm)d _{i}(cm)image orientation image type f (cm) 140 120 40 20

- Results:

Calculate the focal distance of the lens by averaging your results. Give the power of the lens in diopters.

f _{1}(cm)f _{2}(cm)f _{3}(cm)f _{4}(cm)f _{average}(cm)P (D)

- Additional Settings:

Last modified: Wed Apr 16 12:20:18 Eastern Daylight Time 2008