Chapter 17, Problem 91A

To determine

The focal length of the concave mirror.

Answer to Problem 91A

  $11\text{cm}$

Explanation of Solution

Given:

The given figure is

  

The object distance from the mirror, $d_o=22\text{cm}$

The image distance from the mirror, $d_i=22\text{cm}$

Formula used:

Mirror equation,

  $\frac{1}{f}=\frac{1}{d_i}+\frac{1}{d_o}$

Where,

  $\begin{array}{l}f=\text{focal length}\\ d_i=\text{ image distance}\\ d_o=\text{object distance}\end{array}$

Calculation:

Using the given values in Mirror equation, the focal length of the mirror will be,

  $\begin{array}{c}\frac{1}{f}=\frac{1}{d_i}+\frac{1}{d_o}\\ \frac{1}{f}=\frac{1}{22}+\frac{1}{22}\\ f=\frac{22}{2}\\ =11\text{cm}\end{array}$

Conclusion:

Therefore, the focal length of the mirror is $11\text{cm}$ .