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If two + 5 D , lenses are mounted at some distance apart, the equivalent power will always be negative, if the distance is

Options

  1. AGreater than 40   cm
  2. BEqual to 10   cm
  3. CGreater than 8 0 cm
  4. DLess than 10   cm

Correct answer

A. Greater than 40   cm

Step-by-step solution

When two lenses are separated by some distance x , then equivalent power P = P ₁ + P ₂ - x P ₁ P ₂ ∴ P = 5 + 5 - x × 5 × 5 o r   P = 10 - 25 x Power P will be negative if 10-25x will be negative i e ,         25 x > 10 o r     x > 10 25 o r     x > 10 25 × 100   cm o r     x > 40   cm

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