Q27 of 284 Page 262

The power of a combination of two lenses X and Y is S D. If the focal length of lens X be 1S cm :

(a) calculate the focal length of lens Y.


(b) state the nature of lens Y.

Power of combination = 5 D

Focal length of X = 15 cm= 0.15 m


Power of X = 1/ 0.15 = 6.67 D


(a) Power of Y = 5 – 6.67 = -1.67 D


f = 1/P = - 60 cm


(b) Nature of lens is Concave lens


More from this chapter

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25

A convex lens of power S 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 ?

 26

A convex lens of focal length 2S cm and a concave lens of focal length 10 cm are placed in close contact with one another.

(a) What is the power of this combination?


(b) What is the focal length of this combination?


(c) Is this combination converging or diverging ?

 28

Two lenses A and B have focal lengths 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?


(c) What is the power of combination if lenses A and B are held close together?

 29

What do you understand by the power of a lens ? Name one factor on which the power of a lens depend.