# A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

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A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

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Here, f_1=40cm , f_2= -25cm,P=?
Clearly, P_1=(100)/(f_(1))=(100)/(40)=2.5D
and P_(2)=(100)/(f_(2)) = (100)/(-25)= -4.0D
As P=P_1+P_2, P=2*5 - 4*0= -1.5D

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