A convex lens of focal length 40cm and refractive index 32 is placed in a medium of refractive index 53, then
It will act as a convergent lens of focal length 100cm
It will act as a divergent lens of focal length 100 cm
It will act as a divergent lens of focal length 200 cm
It will act as a convergent lens of focal length 200cm
A
It will act as a convergent lens of focal length 200cm
B
It will act as a divergent lens of focal length 100 cm
C
It will act as a divergent lens of focal length 200 cm
D
It will act as a convergent lens of focal length 100cm
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Solution
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LENS MAKERS FORMULA :
When a lens is immersed in a liquid: 1f1=(μgμl−1)(1R1−1R2)
Where μg = refractive index of lens
f = focal length of lens in air
f1 = focal length of lens in liquid
The new focal length f1 is given by:
f1f=(μg−1)(μgμl−1);
Given: μl=53,μg=32
Substituting in the formula mentioned in the concept,
f1f=32−13×32×5−1=−5
f1=−5×f=−5×40=−200cm
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