Question

An object is placed at principal axis of a concave lensat a distance of 20cm fromit andif thefocal length of thelensis also 20cm, find thelocation of the image

Answer 1

Dear Student,

According to the question,

$$\begin{gathered} u=-20\mathrm{cm} \\ f=-20\mathrm{cm} \\ v=? \\ \mathrm{Using}\mathrm{lens}\mathrm{formula} \\ \frac{1}{v}-\frac{1}{u}=\frac{1}{f} \\ \frac{1}{v}-\frac{1}{(-20)}=\frac{1}{(-20)} \\ \frac{1}{v}=\frac{1}{(-20)}-\frac{1}{20} \\ \frac{1}{v}=\frac{-20-20}{400} \\ \frac{1}{v}=\frac{-40}{400} \\ v=-10\mathrm{cm} \end{gathered}$$
Location of the image is 10 cm towards the left side of the lens.

Regards