Question

An object is placed at 15 cm in front of convex lens of focal length 10 cm. Where shall we place a convex mirror of focal length 13 cm so that real image and object coincide?

• A. 6 cm from lens
• B. 3 cm from lens
• C. 4 cm from lens
• D. 2 cm from lens

Answer 1

The correct option is C 4 cm from lens

From lens formula, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\Rightarrow \frac{1}{v}=\frac{1}{10}-\frac{1}{15}$

or $v=30cm$.

In order the ray to retrace the path, the ray must be incident normal on the mirror. Hence distance of mirror from $I^{{}^{\prime }}$ should be equal to $R=2f=26cm$ or $4cm$ from lens.