Convex lens in water: focal length: MCQ with Answer and Explanation

Convex lens in water: focal length:
A. Becomes negative
B. Increases
C. Unchanged
D. Decreases
Answer: Option B
Solution (By JKSSB Mock Tests)
Lens maker: 1/f ∝ (n_rel - 1). In water, n_rel = n_glass/n_water ≈ 1.5/1.33 ≈ 1.13 < 1.5 (air). Smaller (n_rel-1) ⇒ larger f. Memory aid: 'Lens in denser medium: reduced power ⇒ longer focal length'. Optics application frequently tested in competitive exams.

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Correct Answer: Option C


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