Question

Q. The focal length of a concave mirror is f and the distance from the object to the principle focus is x. Find the ratio of the size of image to the size of the object.

Answer 1

Dear Student,


$$\begin{gathered} u=-\left(f+x\right) \\ thequestionisaskingformagnification. \\ \frac{1}{v}+\frac{1}{u}=\frac{1}{f} \\ forconcavemirror \\ \frac{1}{v}+\frac{1}{-\left(f+x\right)}=-\frac{1}{f} \\ \frac{1}{v}=\frac{1}{\left(f+x\right)}-\frac{1}{f}=\frac{-x}{f\left(f+x\right)} \\ m=\frac{-v}{u}=\frac{{\displaystyle \frac{f\left(f+x\right)}{x}}}{f+x}=\frac{f}{x} \\ Regards \end{gathered}$$