A convex lens of power 5D and a concave lens of power 7.5D are placed in contact with each other. What is the:
- Power of this combination of lenses?
- Focal length of this combination of lenses?
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$P_1=+D, P_2=-7.5 D$
a. Power of combination,
$P=P_1+P_2$
$=+5 D+(-7.5 D)=-2.5 D$
b. Focal length of the combination,
$f=\frac{1}{P}=\frac{1}{-2.5}=-0.4 m=-40 cm$
a. Power of combination,
$P=P_1+P_2$
$=+5 D+(-7.5 D)=-2.5 D$
b. Focal length of the combination,
$f=\frac{1}{P}=\frac{1}{-2.5}=-0.4 m=-40 cm$
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