A convex lens of refractive index 32 has a power of 2.5 D in air. If it is placed in a liquid of refractive index 2, then the new power of the lens is:
- 1.25 D
- 1.5 D
1.25 D
1.5 D
A
1.25 D
B
- 1.25 D
C
- 1.5 D
D
1.5 D
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Solution
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According to Lens Maker's Formula,
Power of lens=P=(μr−1)(1R1−1R2)
where μr is the refractive index of material of lens relative to the surrounding medium=μmaterialμmedium
For convex lens in air, μr=3/21=32
For convex lens in the liquid, μr=3/22=34
Thus P2P1=μr2−1μr1−1
=34−132−1=−12
⟹P2=−12×2.5D=−1.25D
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