When the object is at distance `u_(1)`and`u_(2)`the images formed by the same lens are real and virtual respectively and of the same size.Then focal length of the lens is:

When an object is at a distance u_(1)andu_(2) from a lens, real image and a virtual image is formed respectively having same magnification. The focal length of the lens is

When an object is at distances x and y from a lens, a real image and a virtual image is formed respectively having same magnification. The focal length of the lens is

When an object is at distances x and y from a lens, a real image and a virtual image is formed respectively having same magnification. The focal length of the lens is

When an object is at a distance u_(1) and u_(2) from the optical centre of a lens, a real and virtual image are formed respectively, with the same magnification.The focal length of lens is:

When the object is at distance u_1 and u_2 from the optical centre of a convex lens, a real and a virtual image of the same magnification are obtained. The focal length of the lens is

When the object is at distance mu_1 and mu_2 from the optical centre of a convex lens, a real and a virtual image of the same magnification are obtained. The focal length of the lens is

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

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