Converging Lens: Real Images Beyond 2f

1 · Predict

An object sits beyond a converging lens's focal length. As you move it farther from the lens, does the real image formed on the other side move closer to the lens or farther away?

• Closer to the lens — a farther object forms its image nearer the focal point.
• Farther from the lens.
• The image distance doesn't depend on object distance.

2 · Set Up

1. Open the converging-real preset and press Reset. The lens's focal length is fixed at 10 cm.
2. Enable the image-distance and magnification readouts.
3. Set the object distance for each trial and record the image distance and magnification.

3 · Collect Data

Plot 1/d_i (y-axis) against 1/d_o (x-axis) for your three trials. Is the line straight?

4 · Analyze

1. For one trial, compute d_i from 1/f = 1/d_o + 1/d_i using f = 10 cm, then m = −d_i/d_o. Compare both to the table.
2. Explain, using the thin-lens equation, why moving the object farther from the lens (increasing d_o) makes the image distance shrink toward the focal length.

5 · Extend

1. Every trial gives a negative magnification. Explain what a negative m means physically for the orientation of the image compared to the object.
2. A camera lens forms a real image on the sensor for any object beyond the focal length. Explain, using your data, why photographing something very far away (d_o ≫ f) always places the image very close to the focal plane.

The Physics Behind This Experiment

← Back to experiment