Lenses — Prelims Questions

A convex lens of focal length $20\,\text{cm}$ is placed in contact with a concave lens of focal length $25\,\text{cm}$. The power of the combination is:

An object is placed at a distance of $15\,\text{cm}$ from a convex lens of focal length $10\,\text{cm}$. The nature and position of the image formed will be:

A biconvex lens has radii of curvature $20\,\text{cm}$ and $30\,\text{cm}$. If the refractive index of the lens material is $1.5$, what is its focal length when placed in air?

Which of the following statements is true for a concave lens?

A lens is placed in a medium whose refractive index is greater than the refractive index of the lens material. What will happen to a convex lens placed in such a medium?

An object is placed $5\,\text{cm}$ in front of a convex lens of focal length $10\,\text{cm}$. What is the magnification produced?