Question

Focal length of a convex lens will be maximum for

• A. yellow light
• B. violet light
• C. blue light
• D. red light

Hint:

Higher wavelength → lower refractive index → larger focal length.

Answer 1

The Correct Option is D

Step 1: Relation between focal length and wavelength.
The focal length of a convex lens depends on the refractive index of the material.
Refractive index decreases as wavelength increases.

Step 2: Compare wavelengths of colors.
Among visible light, red light has the maximum wavelength.
Hence, refractive index is minimum for red light.

Step 3: Conclusion.
Since focal length is inversely related to refractive index, it is maximum for red light.