General Science • PhysicsMedium
What happens to the focal length of a convex lens when it is completely immersed in water?
A. It decreases
B. It remains unchanged
C. It increases✓ Correct Answer
D. It becomes zero
💡 Solution & Explanation
When a convex lens is submerged in water, the refractive index of the surrounding medium rises, reducing the relative refractive index of the glass lens and increasing its focal length. If the surrounding medium matches the refractive index of the lens, the focal length approaches infinity and it behaves like a flat pane. This phenomenon demonstrates that lens focal length depends on both its material and the surrounding fluid medium.
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