A child looks at his reflection in a spherical tree ornament 12 cm in diameter, and sees an image of his face that is reduced by one-fourth. How far is his face from the ornament?

I don't know what I would do with the given information. I know that M=-q/p and M=1/4. Any help is appreciated!

5 answers

You know the radius of curvature for the sphere, so f = 1/2 radius curvature. Use the magnification relationship M= 1/4, then find di/do = 1/4, and finally, if di=.25do, put that in...

1/di + 1/do= 1/f and solve for do.
Can you check? Thanks!

M=-q/p

q=R/2=6cm/2=3cm

1/4=-3cm/p

p=-12cm
Yes.
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