Q145 / 160 · AP EAMCET 2021 (20 Aug Shift 2) · Physics

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.

  • A
    Both A and R are true and R is a correct explanation for A
  • B
    Both A and R are true but R is not a correct explanation for A
  • C
    A is true, R is false
  • Correct answer
    D
    Both A and R are false

Solution

Focal length of the lens depends upon its refractive index as 1f∝μ-1.

Therefore, the focal length of a lens decreases when red light is replaced by blue light.

Hence, the correct answer is option: 'D'.

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