SAT Subject Physics Practice Question 124: Answer and Explanation

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Question: 124

7. An object is placed 60 cm in front of a concave spherical mirror whose focal length is 40 cm. Which of the following best describes the image?

Nature of image     Distance from mirror

A. (A) Virtual          24 cm
B. (B) Real          24 cm
C. (C) Virtual          120 cm
D. (D) Real          120 cm
E. (E) Real          240 cm

Correct Answer: D


If so = 60 cm and f = 40 cm, the mirror equation tells us that

and, since si is positive, the image is real.

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