A single converging lens is held close to the eye for use as a magnifying glass. For maximum magnify

Question

A single converging lens is held close to the eye for use as a magnifying glass. For maximum magnifying power, the lens must be positioned so that

Professor PC Thomas Classes · Answer

To achieve maximum magnifying power with a magnifying glass (a simple microscope), the image must be formed as close to the eye as possible while remaining clear.

The Two Cases of Magnification:
1. Normal Adjustment (Relaxed Eye): The image is formed at infinity ( $v=\infty$ ). The magnifying power is $m=\frac{D}{f}$.
2. Maximum Magnification (Strained Eye): The image is formed at the near point ( $v= -D$, usually $\mathbf{2 5 ~ c m}$ ). The magnifying power is:
$$
m=1+\frac{D}{f}
$$Since $1+\frac{D}{f}$ is greater than $\frac{D}{f}$, the maximum magnification occurs when the image is at the near point.