Power of Lens — Prelims Questions

A convex lens has a focal length of $50,\text{cm}$. What is its power?

Two thin lenses, one convex with focal length $20,\text{cm}$ and another concave with focal length $40,\text{cm}$, are placed in contact. What is the power of the combination?

A person suffering from myopia uses a corrective lens of power $-1.5,\text{D}$. What is the focal length of this lens?

Which of the following statements about the power of a lens is INCORRECT?

A person needs a lens of power $+0.5,\text{D}$ for correcting their vision. What kind of vision defect are they suffering from, and what type of lens is prescribed?

If a lens of power $+4,\text{D}$ is cut into two identical halves along its principal axis, what is the power of each half?