An object placed \(10 cm\) in front of a convex lens of focal length \(20 cm\) produces an image whose position from the lens is?
A. \(20 cm\) to the right B. \(20 cm\) to the left C. \(10 cm\) to the right D. \(10 cm\) to the left
Correct Answer: B
Explanation
$$ u=10 cm , f=20 cm $$ to find \(v=\) ? using the lens formula i.e. \(\frac{1}{f}=\frac{1}{u}+\frac{1}{v} ; \frac{1}{20}=\frac{1}{10}+\frac{1}{v}\) \(\frac{1}{20}-\frac{1}{10}=\frac{1}{v} ; \frac{1-2}{20}=\frac{1}{v}\) \(\frac{-1}{20}=\frac{1}{v} ; v=-20 cm\) This is a virtual (erect) image which is formed \(20 cm\) to the left of the lens
