## Physics: Principles with Applications (7th Edition)

a. Moving closer to the subject decreases the object distance. The focal length of the lens stays constant. Equation 23-8, $\frac{1}{d_{o}} + \frac{1}{d_{i}} = \frac{1}{f}$, tells us that if $d_{o}$ decreases and f stays the same, the image distance $d_{i}$ must increase. The position of the real image moves farther away from the lens. b. The size of the real image also changes. As the object distance becomes smaller and the image distance becomes larger, the magnification, $m=-\frac{d_{i}}{d_{o}}$, becomes larger. The size of the image increases.