Question

What is the position of image when an object is placed at a distance of 10 cm from a convex lens of focal length 10 cm?

Answer 1

Given:
Object distance, u = $-$10 cm
(Since object is always placed on the left side of lens)
Focal length, f = +10 cm
According to lens formula:
$$\begin{gathered} \frac{1}{\mathrm{v}}-\frac{1}{\mathrm{u}}=\frac{1}{\mathrm{f}} \\ \frac{1}{\mathrm{v}}=\frac{1}{\mathrm{f}}+\frac{1}{\mathrm{u}} \\ \frac{1}{\mathrm{v}}=\frac{1}{10}+(-\frac{1}{10})=0 \\ \mathrm{v}=\frac{1}{0}=\infty \end{gathered}$$
Therefore, the position of image will be at infinity.