Question 17.2: Sample Exercise: A Virtual Magnified Image An object 2 cm in...
Sample Exercise: A Virtual Magnified Image
An object 2 cm in height lies 10 cm to the left of a positive lens with a focal length of 20 cm.
a. Where is the image located?
f = +20 cm
o = +10 cm
i = ?
b. What is its magnification?
m = ?
\frac{1}{o}+\frac{1}{i}=\frac{1}{f}
\frac{1}{i}=\frac{1}{f}-\frac{1}{o}
=\frac{1}{20 cm}-\frac{1}{10 cm}
=\frac{1}{20 cm}-\frac{2}{20 cm}
=-\frac{1}{20 cm}
i = -20 cm
The image lies 20 cm to the left of the lens, on the same side as the object (fig. 17.17).
b.
m=-\frac{i}{o}=-\frac{20 cm}{10 cm}
= +2
The image is magnified to twice the height of the object as shown in figure 17.17. It is upright, since the magnification is positive.
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