Question

A simple microscope is rated $5\text{X}$ for a normal relaxed eye. What will be its magnifying power for a relaxed farsighted eye whose near point is $50\text{cm}$ ?

• A. $5\text{X}$
• B. $8\text{X}$
• C. $10\text{X}$
• D. $12\text{X}$

Answer 1

The correct option is C $10\text{X}$

Given, magnifying power, $m=5\text{X}$ for normal relaxed eye.

We know for relaxed eye,

$m=\frac{D}{f}$

Where, $D$ is the least distance of distinct image for the person.

$\Rightarrow 5=\frac{25}{f}$ $(\because D=25\text{cm})$

$\therefore f=5\text{cm}$

For person whose near point is $50\text{cm},i.e,D=50\text{cm}$

$\therefore$ Magnifying power,

$m=\frac{D}{f}=\frac{50}{5}=10\text{X}$

Hence, $\left(C\right)$ is the correct answer.

Why this Question: Concept: Magnifying power of a simple microscope for relaxed eye depends on near point of the eye and focal length of the microscope.