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  1. Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of the lens when immersed in a liquid of refractive index of 1.25 will be
    1. 10 cm
    2. 2.5 cm
    3. 5 cm
    4. 7.5 cm
Correct Option: C

fa
 =
μg
 - 1 =
1.5
 - 1
μl1.25
fl(μg - 1)(1.5 - 1)

=
1
5 =
2
1
5
2

fl =
5
fa =
5
 × 2 = 5 cm
22


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