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Old Mar 31st 2009, 06:25 PM   #1
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concave mirror

I keep getting the wrong answer to this problem. I'm sure I'm making a stupid mistake somewhere, but can't figure out what's wrong. I'd really appreciate any help.

QUESTION:
It is observed that the size of a real image formed by a concave mirror is four times the size of the object when the object is 30.0 cm in front of the mirror. What is the radius of curvature of this mirror?

ATTEMPT:
M = -Xi/Xo = -4
Xi = 4Xo
1/Xo + 1/(4Xo) = 1/f
f = 4/5 Xo
3Xo = 0.3m
f= 4/5 (0.1)
= 0.08
R = 2f = 2(0.08) = 0.16

I know I'm doing something wrong here...
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Old Mar 31st 2009, 07:11 PM   #2
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Object distance u = Xo = -30
Image distance v =4Xo = -120
-1/30 - 1/120 = 1/f
f = -24 cm
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Old Mar 31st 2009, 09:12 PM   #3
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thank you

Thanks a lot Parvez! I see where I was messing up. Now to calculate the radius of curvature, I just take 2F (2 x 24 in this case)

Thanks again!!
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