Posted by Emily on .
An image of a candle is produced by a convex lens 14 cm away. If the focal length of the lens is 7 cm, how far from the lens is the candle placed?
(USe the thin lens equation)
For this question, how would you know whether the image is virtual or real?(in order to know if the distance to the mirror is negative or positive)

Physics 
drwls,
Solve
1/do + 1/di = 1/do + 1/14 = 1/f = 1/7
The answer is that the object distance is (do) = 14. You get a 1:1 real image.
The image is real because do is positive.