Two convex lenses with power 2 dioptre are kept in contact

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Two convex lenses with power 2 dioptre are kept in contact with each other. The focal length of the combined lens system is

1. 0.10 m
2. 2 m
3. 4 m
4. 0.25 m

Answer

The power of combination of lenses is the algebraic sum of the powers of individual lenses.

P = P₁ + P₂ = 4 m

1/f = 1/f₁ + 1/f₂

f = 1/4 = 0.25 m

The correct option is D.