Physics Question 41 – NEET-UG 2023

The system is equivalent to a liquid block (zero power) with a glass lens replacing a liquid lens of the same shape. The net power is the difference between the powers of the glass and liquid lenses in air, which quickly yields $P_{eq}=P_{glass}-P_{liquid}=\frac{1}{20}-\frac{3}{50}=-\frac{1}{100}$ cm⁻¹, giving $f_{eq}=-100$ cm.