Two convex lenses of powers `4D` and `6D` are separated by a distance of `(1)/(6)m` . The power of the optical system so formed is

Two convex lenses of power 2 D and 3 D are separated by a distance 1/3m . The power of the optical system formed is

Two convex lesses of power 2 D and 5 D are separated by a distance 1/3m m The power of the optical system formed is

Two convex lenses of focal lengths f_(1) and f_2 are separated co-axially by a distance d. The power of the combination will be one if

Two convex lenses of focal length f_1 and f_2 are mounted coaxially separated by a distance. If the power of the combination is zero, the distance between the lenses is

Two convex lenses of focal length f_1 and f_2 are mounted coaxially separated by a distance. If the power of the combination is zero, the distance between the lenses is

Two coaxial lenses of power + 4D and - 2D are placed in contact. The focal length of combination is

Two convex lenses with power 2 dioptre are kept in contact with each other. The focal length of the combined lens system is

Two lenses having focal lengths +0.20 m and -0.30 m are separated by a distance of 0.15 m. Find the resultant power of the combination.

Two thin convex lenses of focal lengths f_1 and f_2 are placed at a distance d between them. For the power of combination to be zero, the separation d should fee :