Two lenses of power 15D and -3D are placed in contact. The focal length of the combination is a
Two lenses of power 15D and -3D are placed in contact. The focal length of the combination is a
A. 10cm
B. 15cm
C. 12cm
D. 18cm
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Correct Answer - D
`"Given" P_(1)=15D and P_(2)=-3D`
`therefore P=P_(1)+P_(2)=15D-3D=12D `
`therefore P=(1)/(f(m)) Rightarrow P=(100)/(f(cm)) Rightarrow 12=(100)/(f)`
Focal length of the combination, `f=(100)/(12)=8.33cm`
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