Read Lens–Mirror Systems: Trace the Image Twice
A plane mirror does not add optical power, but it reverses the travel direction. Treat the light as two lens passages separated by reflection at the mirror plane.
Lens and Plane-Mirror Double Pass is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Start with the condition
First locate the one-pass lens image with the Cartesian sign convention. Reflect that image in the mirror, then use the reflected object position for the second passage through the lens.
Build the governing relation
A final image at the mirror plane is a geometric condition on the double pass. Check the stated mirror distance in the second lens equation before deciding whether the image is real or virtual.
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.
Using the first lens image as the final image ignores the reflected second pass through the lens.
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