Question 22
Lenses and Optical InstrumentsIf the magnification of a virtual image formed of an object 10 cm from a convex lens is 3, then the focal length of the lens is
- A.10 cm
- B.15 cm
- C.16 cm
- D.19 cm
- E.20 cm
Show the answer and explanation
Answer: B (15 cm)
Explanation
The virtual image is 3 × 10 = 30 cm away on the same side (v = −30 cm). 1/f = 1/10 − 1/30 = 2/30, so f = 15 cm.