- #1
Overdose_
- 3
- 2
- Homework Statement
- A candle, a converging lens and a white screen are placed in a line with the lens between the candle and the screen. A distance of 72cm separates the candle and screen. As the lens is moved to all points between the candle and the screen, only one focused image of the candle can be made on the screen. What is the focal length of the converging lens?
- Relevant Equations
- The thin lens equation
This is the solution but I do not understand??? How could they just assume the object distance equals 2f? No magnification is given here.
We know the candle produces a real image and the distance is limited, so that means it must be somewhere between the principal focus, the center of curvature, and possibly a little beyond that. Doesn't that mean, then, that the object distance can be anywhere between 2 point something f to 1f? Only one image is produced, what if that ONE image isn't produced at 2f? Then wouldn't the assumption be invalid? What? Please help