Question

Name the lens which is used in wide angle spyhole in doors.

Answer 1

Concave lens is used in peep-holes. Concave lens curve inwards so when the light rays pass through them, light rays come together making the objects appear smaller than they really are. When you look through the spy-hole, it shows the whole area and the person knocking.

Answer 2

Concave lens also known as Diverging lens  is used in wide angle spyhole in doors.

Working Mechanism :
-->A peep hole or door viewer is a small opening through a door allowing an individual to look from the inside to the outside .
--->A lens is fitted in such way that it allows the wider field view from the inside and little to no visibility from outside.
--->  concave lens is mounted in such a way that it gathers Light rays from angles on the outside of the door and tries to focus them on a small pupil sized region on the inside of the door.