Final answer:
To increase the magnification from 3.0 to 4.0 for an object positioned to the left of a convex lens, the object should be moved closer to the lens. This is because magnification for virtual images increases as the object distance decreases.
Step-by-step explanation:
To increase the magnification from m = 3.0 to m = 4.0 for an object positioned to the left of a convex lens with a focal length of 34 cm, we need to understand the relationship between object distance, lens focal length, and magnification. The lens formula 1/f = 1/do + 1/di combined with the magnification equation m = -di/do provides the needed insights. Since the magnification is positive, we know we are dealing with a virtual image, which occurs when the object is placed within the focal length of the convex lens. Consequently, to increase magnification, the object should be moved closer to the lens.
As an object moves closer to the lens, the distance from the object to the lens (object distance, do) decreases, while the image distance (di) increases in the case of a virtual image.
This change results in an increased magnification (m), as per the magnification equation, since m = -di/do. Therefore, moving the object closer to the lens will increase the magnification to the desired level of 4.0. Based on similar principles, in Example 25.7 from the question context, a book held closer than its focal length to a lens shows an increase in magnification as the object distance decreases.