Calculating the Focal Length of a Concave Mirror

AI Thread Summary
To calculate the focal length of a concave mirror, the problem involves a real image that is 0.756 times the size of the object and a distance of 0.764 m from the mirror to the screen. The relevant equations include the mirror formula and magnification relationships. The user attempted to find the object distance (do) using the magnification formula but arrived at an incorrect focal length of 0.435 m. Clarification on sign conventions and proper application of the equations is needed to determine the correct focal length.
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concave mirror!

Homework Statement



The real image produced by a concave mirror is found to be 0.756 times the size of the object. If the distance from the mirror to the screen on which the image appears is 0.764 m , what is the focal length of the mirror?

Homework Equations



(a) 1 /do + 1/di = 1/f

(b) image height / object height=m = - di/do

(c) - object height / image height = do / di

The Attempt at a Solution


m= 0.756 = -hi / ho

so to use equation "c"

i inverted --- > -1/0.756
then set it euqal to rest of the equation so --> -1/.756 = do / .764
do= -1.01058 m

then i used equation "a"

(1/-1.01058) + (1/.764) = 1/f and solved for f

Answer was Wrong. Please tell me what I need to do. Thank you!
 
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I got the answer 0.435 m. Is it correct? If so check your sign convention.
 
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