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## Example 13.3: Converging lenses

Question: An object of height cm is placed a distance cm in front of a thin converging lens of focal length cm. What is the height, location, and nature of the image? Suppose that the object is moved to a new location a distance cm in front of the lens. What now is the height, location, and nature of the image?

Answer: According to Eq. (367), the image distance is given by

Thus, the image is virtual (since ), and is located cm in front of the lens. According to Eq. (10.24), the magnification of the image is given by

Thus, the image is upright (since ), and magnified by a factor of . It follows that the height of the image is given by

If the object is moved such that cm then the new image distance is given by

Thus, the new image is real (since ), and is located 57.27cm behind the lens. The new magnification is given by

Thus, the image is inverted (since ), and diminished by a factor of . It follows that the new height of the image is

Note that the height is negative because the image is inverted.

Next: Example 13.4: Diverging lenses Up: Paraxial Optics Previous: Example 13.2: Convex mirrors
Richard Fitzpatrick 2007-07-14