Two thin converging lenses of focal length 15 cm and 30 cm are held in contact with each other. The focal length of the combination is

Two thin converging lenses of focal lenths 15 cm and 30 cm are held in contact with each other.Calculate power and focal length of the combination.

Two convex lenses of focal lengths 25 cm and 15 cm are placed in contact with each other. Find the focal length of combination.

Two lenses of power -15D and +5 D are in contact with each other. The focal length of the combination is

Two lenses of power -15D and +5 D are in contact with each other. The focal length of the combination is

When two thin converging lenses of focal lengths f, and f, are held in contact with each other, calculate the power of the combination.

Two lenses of power - 15 D and + 5 D are in contact with each other. The focal length of the combination is

Two thin lenses of power + 3 D and - 1 D are held in contact with each other. Focal length of the combination is :