Question:
The focal length of a convex lens is minimum for:
The focal length of a convex lens is minimum for:
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$f_{red}>f_{violet}$ because $\mu_{violet}>\mu_{red}$.
Updated On: Apr 8, 2026
- red light
- violet light
- yellow light
- green light
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The Correct Option is B
Solution and Explanation
Step 1: Concept
According to Lens Maker's Formula, $1/f = (\mu - 1)(1/R_{1} - 1/R_{2})$.
Step 2: Analysis
Refractive index ($\mu$) is higher for shorter wavelengths (Cauchy's equation). Violet light has the shortest wavelength in the visible spectrum, so it has the highest $\mu$.
Step 3: Conclusion
Since $f$ is inversely proportional to $(\mu - 1)$, the focal length is minimum for violet light.
Final Answer: (B)
According to Lens Maker's Formula, $1/f = (\mu - 1)(1/R_{1} - 1/R_{2})$.
Step 2: Analysis
Refractive index ($\mu$) is higher for shorter wavelengths (Cauchy's equation). Violet light has the shortest wavelength in the visible spectrum, so it has the highest $\mu$.
Step 3: Conclusion
Since $f$ is inversely proportional to $(\mu - 1)$, the focal length is minimum for violet light.
Final Answer: (B)
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