Physics Review Question

Unit: Geometrical Optics Year: 1997 Question#: 87
Question: A spherical mirror that forms only virtual images has a radius of curvature of 0.50 meter. The focal length of this mirror is

(1 ) -0.25 m
(2 ) +0.25 m
(3 ) -0.50 m
(4 ) +0.50 m
What is this question really asking?

Explanation by: Josh S

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Answer 1
-0.25 m


The focal length has an absolute value of one half of the radius of curvature, or the center length of the mirror. The fact that the mirror only creates virtual images indicates that the focal length must be negative. return to top

Answer 2
+0.25 m

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Answer 3
-0.50 m

return to top

Answer 4
+0.50 m


The focal length is one half the radius of curvature, therefore it is not 0.50. Also due to the mirror only creating virtual images, it must be a negative value. return to top

What's this question really asking?

A mirror that ONLY creates images behind itself has a central length of .5 m. What is the focal length of the mirror? return to top

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