In the equation M = uF, what does u represent?

• A. Original distance between object and eye
• B. Distance between object and lens
• C. Focal length
• D. Power of the magnifier

Answer: (A)

The key idea here is how a simple magnifier changes what you see by combining the lens’s power with the distance from the object to the eye. In this relationship, the symbol u stands for the original separation between the object and the eye before you use the magnifier. That baseline distance sets the angular size the eye would perceive, and the lens’s focal power F then modifies that perception to produce the magnified image. The other factors—distance from the object to the lens, the focal length, or the magnifier’s power as a separate quantity—do not describe the baseline object-eye spacing, which is what u represents in this formula.