If a concave mirror with a focal length of 10.0 cm creates a real image 30.0 cm away on its principal axis, how far from the mirror is the corresponding object?
1 Answer
Apr 30, 2014
+15.0 cm.
Explanation:
For this question, we need to use the mirror formula
#\frac{1}{f} = 1/d_o + 1/d_i# .
What the problem gives us is: f = 10.0 cm, and

#\frac{1}{d_o} = \frac{1}{f}  1/d_i# 
#1/d_o = 1/10 1/30# . FInd a common denominator. 
#1/d_o = 3/30  1/30# 
#1/d_o = 2/30# . To find#d_o# , take the reciprocal. 
#d_o = 30/2 = +15.0 cm#
The same process can be used if you know the distance from the object to the vertex of the mirror, and are looking for