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** Up:** Paraxial Optics
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*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