Power of Combination of lenses

Two lenses A and B have focal length of +20 cm and, -10 cm, respectively. a) What is the nature of lens A and lens B? b) What is the power of lens A and lens B? What is the power of combination if lenses A and B are held close together?

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Power and Combination OF Lenses and Mirrors

The power of a converging lens is 4.5 D and that of a diverging lens is 3 D. The power of this combination of lenses placed close together is:

A convex lens of power 5 D and a concave lens of power 7.5 D are placed in contact with each other. What is the: a) power of this combination of lenses? b) focal length of this combination of lenses?

Shashank went to the optician to get his eyes checked. He observed that the doctor combined two lenses and put these in front of his eyes so that he could see clearly. The powers of the two lenses used in the combination were -3 D and 4 D. Which of these will be the focal length of the combination of lenses Shashank has to wear?

A convex lens and a concave lens, each having same focal length of 25 cm , are put in contact to form a combination of lenses. The power in diopters of the combination is

The power of a combination of two lenses X and Y is 5 D. If the focal length of lens X be 15 cm: a) Calculate the focal length of lens Y. b) State the nature of lens Y.

It is desired to make an achromatic combination of two lenses, (L_(1)& L_(2)) made of materials having dispersive power omega_(1) and omega_(2)(ltomega_(1)) . If the combination of lenses is converging then: