SAT Subject Physics Practice Question 126: Answer and Explanation

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Question: 126

9. The image created by a converging lens is projected onto a screen that’s 60 cm from the lens. If the height of the image is the height of the object, what’s the focal length of the lens?

A. 36 cm
B. 45 cm
C. 48 cm
D. 72 cm
E. 80 cm

Correct Answer: C


Since the image is projected onto a screen, it must be real, and therefore inverted. The magnification must be negative, so

Because si = 60 cm, the object distance, so, must be 240 cm. Therefore

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