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Assertion (A): The focal length of lens does not change when red light is replaced by blue light. Reason (R): The focal length of lens does not depend in colour of light used.

Options

  1. ABoth A and R are true and R is a correct explanation for A
  2. BBoth A and R are true but R is not a correct explanation for A
  3. CA is true, R is false
  4. DBoth A and R are false

Correct answer

D. Both A and R are false

Step-by-step solution

Focal length of the lens depends upon its refractive index as 1 f ∝ μ - 1 . Therefore, the focal length of a lens decreases when red light is replaced by blue light.

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