Question 27
Lenses and Optical InstrumentsWhat must be the distance between an object and a converging lens of focal length 20 cm to produce an erect image two times the object height?
- A.20 cm
- B.15 cm
- C.10 cm
- D.5 cm
Show the answer and explanation
Answer: C (10 cm)
Explanation
An erect, magnified image is virtual, with v = −2u. 1/u − 1/(2u) = 1/20 gives 1/(2u) = 1/20, so u = 10 cm.