Before you touch the controls
Start with the object more than two focal lengths from the lens. Predict whether moving it closer will make the image larger or smaller, and where the screen will need to move.
Change one thing at a time
- Open the lab with a converging lens. Choose a focal length and keep it fixed throughout.
- Place the object beyond twice the focal length. Move the screen until the image is in focus. Record object distance, image distance and image orientation.
- Repeat at three more object distances, keeping the object outside the focal point. Use the notebook to record each trial.
- Move the object inside the focal length. Inspect the virtual image and explain why it cannot be caught on the screen.
Record your observations
| Object distance u | Image distance v | Magnification | Real or virtual? |
|---|---|---|---|
| Trial 1 | — | — | — |
| Trial 2 | — | — | — |
| Trial 3 | — | — | — |
| Trial 4 | — | — | — |
Use this table as a worksheet, or record the available measurements in the lab notebook. Export your observations before refreshing or closing the lab.
Turn measurements into an explanation
- Use 1/f = 1/u + 1/v for real object and real image distances. Does your data agree?
- What happens to image distance as the object approaches the focal point from outside?
- Why does the image become upright and virtual when the object is inside the focal point?
Think about the model
This is a thin-lens model. Real lenses have thickness, aberrations and alignment errors. The simulation is useful for relationships, not a complete optical design.
Take it further
Switch to a diverging lens and compare image orientation, size and location. State the sign convention before applying the lens equation.