Solved: PHYSICS Question for NEET

NEET PHYSICSMedium

In the figure shown here, what is the equivalent focal length of the combination of lenses? (Assume that all layers are thin)

-50 cm

40 cm

-40 cm

-100 cm

Identify Components: The problem typically involves a combination of lenses (e.g., a convex lens and a liquid layer or multiple solid layers) placed in contact. The equivalent focal length ( $f_{eq}$ ) is found by treating each layer as an individual thin lens.
Lens Maker's Formula: Calculate the focal length ( $f_i$ ) of each individual lens using the formula: $\frac{1}{f_i} = (\mu_i - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$ where $\mu_i$ is the refractive index of the layer and $R_1, R_2$ are the radii of curvature of its surfaces (using proper sign convention).
Combination Formula: For thin lenses in contact, the equivalent focal length is given by: $\frac{1}{f_{eq}} = \frac{1}{f_1} + \frac{1}{f_2} + \dots$
Calculation: By substituting the specific values of $\mu$ and $R$ from the missing figure into the Lens Maker's formula for each layer and summing their powers, one would arrive at the net focal length. Based on the provided probable answer, the result is $-100 \text{ cm}$ .

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