Answer: 10 cm.
- A 5 cm
- B 10 cm
- C 20 cm
- D 40 cm
Correct answer: B. 10 cm
Explanation: f = R/2 = 20/2 = 10 cm. Focal length is half the radius of curvature.
Concave mirror ray construction: a ray parallel to the axis reflects through F, and a ray through F reflects parallel, locating the inverted real image. Image: Maxmath12, CC0, via Wikimedia Commons.
Concept context
Reflection, refraction, lenses, mirrors, total internal reflection.