AIIMS 2017 Physics Lens and Light Assertion Reason Question
Assertion: The focal length of lens does not change when red light is replaced by blue light. Reason: The focal length of lens does not depends upon colour of the light used.
If both assertion and reason are true and reason is correct explanation of assertion.
If both assertion and reason are true and reason is not correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
Correct Answer
Detailed Explanation
The assertion is true because the focal length of a lens is determined by its shape and the refractive index of the material, which remains constant regardless of the light's color. However, the reason is false; the focal length does depend on the wavelength of light due to dispersion, where different colors (e.g., red vs. blue) refract at different angles. Thus, while the assertion stands, the reason does not accurately explain it, making option C the correct choice. Options A and B are incorrect because they assume the reason is true, while option D is incorrect as it dismisses the validity of the assertion.
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