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

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

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

Two lenses of power + 15 D and - 5 D are in contact with each other. What is the focal length of the combination ? What would be the position of image formed by the combination for an object at 30 cm ?

Two lens of power + 15 D and - 5 D are in contact with each other. What is the focal length of the combination ? What would be the position of image formed by the combination for an object at 30 cm ?

If two lenses of power 2D and 3D are kept in contact with each other, then focal length of the combination will be .......... cm.

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

Two lens of power - 12D and + 7D are in contact with each other, the focal length of combination is :