Question

Which of the following can make a parallel beam of light when light from a point source is incident on it?

• A. Concave mirror as well as convex lens
• B. Convex mirror as well as concave lens
• C. Two plane mirrors placed at ${90}^0$ to each other
• D. Concave mirror as well as concave lens

Answer 1

Answer: (A)

When light rays from a point source is incident on concave mirror and convex lens, emergent beams are parallel and the image is formed at infinity.

Convex mirror and concave lens on the other hand always form a virtual image. Emergent beams from these are not parallel but diverging when the object is kept at focus.