Read Lens with Liquid: Track Each Optical Interface
A lens followed by a finite liquid layer is not a single lens in one medium. Form the lens image first, then use refraction at the plane liquid-air boundary.
Lens Imaging Across a Liquid Boundary is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Start with the condition
Use the thin-lens formula for the glass lens in its stated surrounding medium.
Build the governing relation
Carry Cartesian signs through both stages and identify whether the intermediate image lies before or beyond the interface.
Finish with a physical check
Check the limiting case before selecting an option: remove the special feature in the diagram or make the relevant parameter very large or very small. The result should reduce to a familiar relation.
OlympIQ exam lens
- ✓State the physical condition before choosing a formula.
- ✓Keep direction, sign and constraint information explicit.
- ✓Test one limiting case before committing to an option.
Replacing the setup by one effective focal length loses the finite liquid boundary that changes the final image position.
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