There is a hole in the middle of a small thin circular converging lens of focal length `f=4 cm`. The diameter of the hole is half the aperture diameter of lens. There is a point like light source `A=9 cm` from a wall. Where should the lens be placed from object (in cm) in order to get a single circular illuminated spot on the wall which also has a sharp edge ?

For glass lens f=+50 cm. Then power of lens is

An object O is kept infront of a converging lens of focal length 30 cm behind which there is a plane mirror at 15 cm from the lens.

A point object is placed at distance of 20 cm from a thin plane - convex lens of focal length 15 cm . The plane surface of the lens is now silvered . The image created by the system is :-

A converging lens of focal length 20 cm and diameter 5 cm is cut along the line AB . The part of the lens shown shaded in the diagram is now used to form an image of a point P placed 30 cm away from it on the line XY which is perpendicular to the plane of the lens. The image of P will be formed.

The following objects are placed one after each other in given order onto a central axis with a separation of 40 cm each. A point source of light O. a diverging lens of focal length 40 cm. a converging lens of focal length 40 cm and converging mirror of focal length 80 cm. The aperture diameter of lenses and mirror is d=20 cm . If a point source of light is placed at a perpendicular distance of x from central axis then. (You have to consider single optical event at any optical element) Mark the CORRECT statement(s):-

The following objects are placed one after each other in given order onto a central axis with a separation of 40 cm each. A point source of light O. a diverging lens of focal length 40 cm. a converging lens of focal length 40 cm and converging mirror of focal length 80 cm. The aperture diameter of lenses and mirror is d=20 cm. If a point source of light is placed at a perpendicular distance of x from central axis then. (You have to consider single optical event at any optical element) Mark the CORRECT statement(s):-

A biconvex lens of focal length 15 cm is in front of a plane mirror. The distance between the lens and the mirror is 10 cm. A small object is kept at a distance of 30 cm from the lens. The final image is

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is ..........

The focal length of the lens in a photographic camera is 5cm. what is the power of the lens?

Focal length of thin lens ......