Two thin convex lenses of focal lengths 10 cm and 20 cm are placed in contact. Then effective power of the combination is :

Foundation

Physics Foundation

Reflection from spherical mirror

Question

11D

15D

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P = P₁ + P₂
P = $\frac{100}{f_{1}}$ + $\frac{100}{f_{2}}$
= $\frac{100}{10}$ + $\frac{100}{20}$ = 10 + 5 = 15 D