Chapter 25, Problem 21P

To determine

(a) To determine:

The focal length of a magnifier.

Answer to Problem 21P

Solution:

$10\text{cm}$

Explanation of Solution

Given:

$M=3.5X$

Formula used:

$M=1+\frac{N}{f}$

Calculation:

Magnification related to near point and the focal length is given by,

$\begin{array}{l}M=1+\frac{N}{f}\\ N=25\text{cm}\\ \text{3}\text{.5=1+}\frac{25}{f}\\ 2.5=\frac{25}{f}\\ f=10\text{cm}\end{array}$

To determine

(b) To determine:

The focal length referred relaxed eye.

Answer to Problem 21P

Solution:

$7.142\text{cm}$

Explanation of Solution

Calculation:

Magnification referred to relaxed eye is given by,

$\begin{array}{l}M=\frac{N}{f}\\ N=25\text{cm}\\ \text{3}\text{.5=}\frac{25}{f}\\ f=7.142\text{cm}\end{array}$