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Concept · Optics
Lenses (foundational)
thin-lens equation 1/f=1/u+1/v, magnification M=hi/ho=v/u, real vs virtual images
Switches you to Physics
Named traps
9 ways this goes wrong.
Each is a named misconception the questions are built to catch. Open one for the move that tempts, and the fix.
- Converging/diverging lens swappedTreats a concave (diverging) lens as converging, or assigns a positive focal length to a diverging lens.→
- Diverging lens forms real imageExpects a single diverging lens to produce a real image of a real object, when it only forms a virtual, upright, reduced one.→
- Image position misjudgedPlaces the image at the wrong location for an object inside versus outside the focal length of a converging lens.→
- Lens focal-length sign ignoredUses a positive focal length for a diverging lens (or ignores sign conventions for the image distance), so a virtual image is treated as real.→
- Lens image always invertedAssumes a converging lens always inverts the image, ignoring the upright virtual image when the object is within the focal length.→
- Magnification ratio invertedComputes magnification as u/v or object-over-image height instead of M=hi/ho=v/u.→
- Magnification sign ignoredDrops the sign of the magnification, so an inverted (negative M) image is reported as upright.→
- Thin-lens equation misusedAdds object and image distances directly (or sets f=u+v) instead of combining reciprocals in 1/f=1/u+1/v.→
- Virtual image labeled realCalls the enlarged upright image from an object inside the focal length real instead of virtual.→
Key formulas
No formula sheet is matched to this concept yet. Work it from first principles, and watch the traps.
Shaky underneath?
If the concept underneath still feels loose, patch it here before coming back to CSCA questions.
FoundationsPhysics 2 breadth