A point object is placed at a distance of 12 cm from a convex lens on its principal axis. Its image is formed on the other side of the lens at a distance of of 18 cm from the lens. Find the focal length of the lens.

Two point objects are placed on principal axis of a thin converging lens. One is 20cm from the lens and other is on the other side of lens at a distance of 40 cm from the lens. The images of both objects coincide. The magnitude of focal length of lens is :-

A point object O is placed at a distance of 20 cm from a convex lens of focal length 10 cm as shown in figure. At what distance x from the lens should a concave mirror of focal length 60 cm, placed so that final image coincides with the object ?

A point object is kept at a distance of 2 m from a parabolic reflecting surface y^(2) = 2x . An equiconvex lens is kept at a distance of 1.80 m from the parabolic surface. The focal length of the lens is 20 cm . Find the position from origin of the image in cm, after reflection from the surface.

An object is kept at a distance of 16 cm from a thin lens and the image formed is real. If the object is kept at a distance of 6 cm from the same lens, the image formed is virtual. If the size of the image formed are equal, the focal length of the lens will be

A point source of light is kept at a distance of 15cm from a converging lens,on its optical axis.The focal length of the lens is 10cm and its diameter is 3cm ,A screen is placed on the other side of the lens ,perpendicular to the axis of lens,at a distance 20cm from it.Then find the area of the illuminated part of the screen?

A convex lens of focal length f forms an image which is 1/3 times the size of the object. Then, the distance of object from the lends is

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 point - like object is placed at 40 cm distance from a covex lens of 20 cm . Plan mirror is placed behind convex lens at 30 cm . Find the image distance by this combination.

A point object is placed at a diatance of 25 cm from a convex lens of focal length 20 cm. If a glass slab of thickness t and refractive index 1.5 is inserted between the lens and the object, the image is formed at infinity. The thickness t is

A convex lens of focal length 30 cm , a concave lens of focal length 120 cm , and a plane mirror are arranged as shown . For an object kept at a distance of 60 cm from the convex lens, the final image, formed by the combination , is a real image , at a distance of : |"Focal length" | = |"Focal length"| = 30 cm " " =120 cm