SAT Subject Physics Practice Question 127: Answer and Explanation

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Question: 127

10. Which of the following is true concerning a bi-concave lens?

A. Its focal length is positive.
B. It cannot form real images.
C. It cannot form virtual images.
D. It can magnify objects.
E. None of the above

Correct Answer: B

Explanation:

A bi-concave lens is a diverging lens. Diverging lenses (like convex mirrors) have negative focal lengths and therefore cannot form real images. (Notice that D is false; diverging lenses and convex mirrors always form diminished, virtual images, as you can verify using the mirror and magnification equations.)

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