Optics
Converging lens — real image
Object beyond f: a real, inverted image forms on the far side (m = −dᵢ/dₒ).
Form a real image with a converging lens using ray tracing. Adjust object distance and focal length to explore the thin lens equation.
Thin lens imaging
Object beyond f: a real, inverted image forms on the far side (m = −dᵢ/dₒ).
The thin-lens equation 1/f = 1/d_o + 1/d_i locates the image. When d_o > f the image distance is positive, so rays converge to a real image on the far side. The negative magnification sign marks inversion. This preset places the object beyond f so the image is sharp and on the optical bench scale.
- 1/f = 1/d_o + 1/d_i
- m = −d_i/d_o
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
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?
Predictions to weigh
- 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.
Variable roles
What you set:
- Object distance d_o (cm)
What you measure:
- Image distance d_i (cm)
- Magnification m
How the investigation runs
- Open the converging-real preset and press Reset. The lens's focal length is fixed at 10 cm.
- Enable the image-distance and magnification readouts.
- Set the object distance for each trial and record the image distance and magnification.
Governing equation
Thin-Lens Equation — dᵢ = dₒ·f/(dₒ − f)
For a thin lens, object distance, image distance, and focal length are related by 1/f = 1/d_o + 1/d_i. This single equation covers converging and diverging lenses alike, using signed distances.
Lateral Magnification — m = −dᵢ/dₒ
The image's size relative to the object is m = −d_i/d_o. A negative m means an inverted image; |m| > 1 means the image is enlarged.
What the printable worksheet asks students to work out
- 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.
- 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.
Where this shows up beyond the lab
- Every trial gives a negative magnification. Explain what a negative m means physically for the orientation of the image compared to the object.
- 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.
- AP Physics 2 — Unit 13: Geometric Optics
- General High School Physics — Light & optics
- NGSS High School Physics — Wave properties
- Closer or farther?
- Move the object farther
- Capture the image
- Open the data
- Explain your evidence
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.