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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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Answer» `-6.5` D `P_1=(-1)/(f_1)=-(1)/(0.25)=-4D` The power for the concave lens of focal length `f_2` = 40 cm `P_2=(1)/(f_2)=(1)/(0.40)=2.5D` Note : The focal length of concave lens is negative. `therefore` The power of the combination of TWO lens, `P=P_1+P_2=-4.0+2.5=-1.5D` |
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