An object of size $\displaystyle 5$ cm is placed at a distance of $\displaystyle 30$ cm from the optical centre of a converging lens of focal length $\displaystyle 20$ cm. Use lens formula to determine the position and size of the image formed.

Position: \(\displaystyle \frac{1}{v}-\frac{1}{u}=\frac{1}{f}\) \[\begin{gathered} \frac{\mathbf{1}}{v}-\frac{\mathbf{1}}{-\mathbf{3 0}}=\frac{\mathbf{1}}{+\mathbf{2 0}} \\ \frac{1}{v}+\frac{1}{30}=\frac{1}{20}=v=+60 \mathrm{~cm} \end{gathered} \] position is $\displaystyle 60$ cm from the lens Size: \[\begin{aligned} \mathrm{m}= & \frac{\boldsymbol{h} \boldsymbol{i}}{\boldsymbol{h} \boldsymbol{0}}=\frac{\boldsymbol{v}}{\boldsymbol{u}} \\ & =\frac{\mathbf{6 0}}{-3 \mathbf{0}}=-2 \end{aligned} \] \(\displaystyle \mathrm{h}_{\mathrm{i}}=-2 \times 5 \mathrm{~cm}=-10 \mathrm{~cm}\) size of image is $\displaystyle 10$ cm(Enlarged)