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Physics · Light · Converging lens
Focal length of a converging lens
An illuminated object is placed in front of a converging lens, with a screen on the far side. The screen is moved until a sharp, inverted image forms. From u and v, the lens formula 1/u + 1/v = 1/f gives the focal length.
object distance u
screen distance v
30.0 cm · sharp
Results table
| u (cm) | v (cm) | f (cm) |
|---|---|---|
| 25 | — | — |
| 30 | — | — |
| 40 | — | — |
| 50 | — | — |
| 60 | — | — |
Exam-style questions
1. Which equation links u, v and f?
2. When the object is placed at u = 2f, where is the sharp image?
3. Why does the image on the screen appear INVERTED?
4. If u = 30 cm gives a sharp image at v = 30 cm, the focal length is: