Physics quiz question: two lens system

Physics 205B Quiz 2, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 24.1

An upright object is placed 10.0 cm to the left of a converging lens with focal length +15.0 cm. A second converging lens with focal length +4.0 cm is placed 5.0 cm to the right of the first lens. Where is the final image located?
(A) To the left of the first lens.
(B) Between the first lens and second lens.
(C) To the right of the second lens.
(D) (No image would be produced.)

Correct answer: (C)

The object is placed within the primary focal point of the first converging lens, which will result in a virtual image, also located to the left of this lens. This virtual image created by the first lens will then be the object for the second lens, and since the object distance for the second lens is outside its primary focal point, the resulting final image will be a real image, located to the right fo the second lens.

Student responses
Section 70856
(A) : 0 students
(B) : 1 student
(C) : 9 students
(D) : 1 student

Success level: 82%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.20