Two thin lenses power `+15 D and -5 D` are cobined together. Their equilavlent focal length is

Two lenses of power +12 D and -2 D are combined together. What is their equivalent focal length ?

Two lenses of power + 12D and - 2D are combined together. What is their equivalent focal length?

Two lenses of power +12 D and -2D are combined together.What is their equivalent focal length?

Fill in the blank spaces with appropriate answers: Two lenses of powers +4D and -4D are joined together. The focal length of the combination is ____.

Two lenses of power 6 D and – 2 D are combined to form a single lens. The focal length of this lens will be

Two lenses of power 6 D and – 2 D are combined to form a single lens. The focal length of this lens will be

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 thin lenses of power +5 D and -2.5 D are in contact. What is the focal length of the combination ?

Two thin lenses of power +5 D and -2.5 D are in contact. What is the focal length of the combination ?