An object is placed at a distance 24 cm in front of a convex lens of focal length 8 cm.

(a) Real and inverted image is formed.

(b) Given, focal length = 8 cm

Object distance (u) = -24 cm

Image distance (v) = ?

From lens formula —

$$\begin{aligned}\frac{1}{v} - \frac{1}{u} = \frac{1}{f} \\[1em]\end{aligned}$$

Substituting the values in the formula we get,

$$\begin{aligned}\frac{1}{\text{v}} - \frac{1}{-24} = \frac{1}{8} \\[1em] \frac{1}{\text{v}} + \frac{1}{24} = \frac{1}{8} \\[1em] \frac{1}{\text{v}} = \frac{1}{8} - \frac{1}{24}\\[1em] \Rightarrow \frac{1}{\text{v}} = \frac{3 - 1}{24} \\[1em] \Rightarrow \frac{1}{\text{v}} = \frac{2}{24} \\[1em] \Rightarrow \frac{1}{\text{v}} = \frac{1}{12} \\[1em] \Rightarrow v = 12\end{aligned}$$

∴ The image is formed at a distance of 12 cm behind the lens.