Question

An object is placed at 30cm in front of concave lens of focal length 10cm. At what distance from the

lens image is formed ?​

Answer 1

By sign convention ,

Object distance (u) = -30 cm

Focal length (f) = -10 cm

We know that , the general formula of lens is given by

$\large \mathtt{ \fbox{ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} }}$

Thus ,

$\sf \hookrightarrow - \frac{1}{10} = \frac{1}{v} - ( - \frac{1}{30} ) \\ \\ \sf \hookrightarrow \frac{1}{v} = - \frac{1}{30} - \frac{1}{10} \\ \\\sf \hookrightarrow \frac{1}{v} = \frac{ - 10 - 30}{300} \\ \\\sf \hookrightarrow \frac{1}{v} = \frac{ - 40}{300} \\ \\\sf \hookrightarrow v = - \frac{300}{40} \\ \\ \sf \hookrightarrow v = - 7.5 \: \: cm$

Hence , the image is formed at a distance of 7.5 cm from the lens on the left side