Mirror & Lens Formulas

1/v + 1/u = 1/f (mirror); 1/v - 1/u = 1/f (lens).

Concept

Mirror & Lens Formulas is a foundational idea in this chapter. The defining relationship is:

$1/v - 1/u = 1/f$

Sign convention: + for distances measured in direction of incident light.

Worked Application

Apply the formula to a typical problem from your textbook. Identify the knowns, plug into the equation, and check that the units work out. Always sanity-check the magnitude before accepting an answer.

Common Confusions

• Confusing the variables in the formula — re-read the symbol definitions in the chapter.
• Forgetting unit conversions (cm vs m, g vs kg).
• Ignoring sign conventions where direction matters.

Key Takeaways

• Master the formula $1/v - 1/u = 1/f$ and one canonical example.
• See the chapter index for full derivations, traps and exam-grade problems.