A thin convex lens of focal length $18,\text{cm}$ forms an image of an object placed $45,\text{cm}$ from the lens. Find the image distance $v$ (in cm).

Step-by-step solution

1. Use the thin lens formula $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$ with $f=18\text{cm}$ and $u=-45\text{cm}$ (object on left is negative).
2. Compute $\frac{1}{v}=\frac{1}{18}-\frac{1}{45}=\frac{45-18}{810}=\frac{27}{810}=\frac{1}{30}$.
3. Thus $v=30\text{cm}$.

Concept tested: Thin lens equation

Published 17 September 2026 · How this solution was prepared and checked