Answer:
13.3 cm
Step-by-step explanation:
You want the image distance from a concave mirror with a focal length of 5 cm when the object is a candle located 8 cm from the mirror.
Mirror relation
The relationship between object, image, and focal distance is ...
1/u +1/v = 1/f
where u and v are the object and image distances, and f is the focal length of the mirror.
For u = 8 and f = 5, this becomes ...
1/8 +1/v = 1/5
1/v = 1/5 -1/8 = 3/40
v = 40/3 = 13 1/3 ≈ 13.3 . . . cm
The image distance is about 13.3 cm.
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Additional comment
In the attached diagram, you may notice the rays are reflected from the plane of the mirror, not the mirror surface. This is the way 'u' and 'v' and 'f' are defined, so is the way the equation works out.
We have rounded the final answer to the nearest tenth, because that is how the given distances are specified.
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