Two similar thin equi-convex lenses of focal length f each are kept coaxially in contact with each other, such that the focal length of the combination is F 1 . When the space between the two lenses i

Question

Two similar thin equi-convex lenses of focal length $f$ each are kept coaxially in contact with each other, such that the focal length of the combination is $F_{1} .$ When the space between the two lenses is filled with glycerin (which has the same refractive index ( $μ = 1.5$ ) as that of glass), then the equivalent focal length is $F_{2} .$ The ratio $F_{1} : F_{2}$ will be

Options:

Answer:

B

Solution:

Case I:

$\frac{1}{F_{eq}} + \frac{1}{F} + \frac{1}{F}$
$F_{1} = F_{eq} = \frac{F}{2}$
Case II:

$F_{2} = F_{eq} = F$
$F_{1} : F_{2} = 1 : 2$

TestHub · Accepted Answer

Case I: 1 F eq + 1 F + 1 F F 1 = F eq = F 2 Case II: F 2 = F eq = F F 1 : F 2 = 1 : 2

Physics - Geometrical Optics Question with Solution | TestHub

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