Pinhole ray projection
Trace straight rays through a pinhole and locate an inverted image on paper.
Adult planning suggestion: about 9–12 · Shape & spatial thinking
- Players
- 3 per group
- Time
- 20–30 minutes
- Materials
- Printed record sheet, pencil and paper markers
Prepare
On the coordinate sheet put the aperture at(0,0), object plane x=−4 and screen x=2. The object’s bottom is(−4,0), top(−4,4). Use a ruler and pencil; no lamp, pin, laser or real camera is required.
Follow the rule
Draw a straight line from each object point through the aperture and extend it to the screen. Do not reflect it at the hole or bend it to stay above the axis. The screen is behind the aperture on the opposite side.
Check each step
Use similar triangles or count the horizontal distance ratio 2/4. The image height coordinate is y_image=−(2/4)y_object. Distances are diagram units, not a claim about an actual printed millimetre scale.
Worked example
The bottom projects to(2,0), top to(2,−2): the image is inverted and half the height. A second object point(−4,2) projects to(2,−1), not(2,1). Keep all three construction lines.
Finish and adapt
Finish when each line passes through its object point, the origin and the marked screen point. Rotate ruler holder, recorder and checker. A thicker real aperture would introduce blur not modeled here; this is a ray diagram, not a completed physical optics experiment.
Purpose, observation and provenance
Within this activity: Trace straight rays through a pinhole and locate an inverted image on paper.
Observe whether the ray stays straight and the screen image crosses to the opposite side of the axis.
Our rules, examples and printable diagrams are separately prepared. The earliest inventor of the broader mechanism is not established here.
Institute of Physics: pinhole camera — Technical background, not an evaluated primary-school lesson. This paper exercise and examples are our adaptation; age and support are adult planning suggestions.
Secondary practice: Cooperation and explaining a check.
For a class of 30, use ten groups of three. Prepare one player-material set per group and keep the host key with the adult. Rotate operator, recorder and checker after each worked example; a reader or scribe may help without choosing answers. Avoid public ranking or diagnostic labels.
Age bands are planning suggestions. Background references may address older learners and do not validate suitability for this age band. Goals describe observable actions, not measured long-term gains or institutional endorsement.
Free alternative: Copy the supplied grids, labels and cards onto reused paper. No specialist product is needed. Adults may prepare pieces or act as a scribe.
Printable materials
Preview at 100% scale, with browser headers and footers off. Cut with suitable help. Keep host keys separate. This is a manual tabletop kit, not an online opponent, automatic judge or solver.
Pinhole ray projection · Player sheet
Before you begin
- On the coordinate sheet put the aperture at(0,0), object plane x=−4 and screen x=2. The object’s bottom is(−4,0), top(−4,4). Use a ruler and pencil; no lamp, pin, laser or real camera is required.
- Draw a straight line from each object point through the aperture and extend it to the screen. Do not reflect it at the hole or bend it to stay above the axis. The screen is behind the aperture on the opposite side.
- Use similar triangles or count the horizontal distance ratio 2/4. The image height coordinate is y_image=−(2/4)y_object. Distances are diagram units, not a claim about an actual printed millimetre scale.
| Object point | Screen point |
|---|---|
| (−4,0) | |
| (−4,2) | |
| (−4,4) |
Pinhole ray projection · Host key — keep separate
Object heights 0,2,4 project to screen heights 0,−1,−2.
What to observe
Observe whether the ray stays straight and the screen image crosses to the opposite side of the axis.
Use the three-person roles described in the rules; offer reading or writing support without selecting answers.
Read the rules as well as this example. Other valid solutions may exist for the puzzle boards. This key is not a claim of uniqueness or measured learning gains.
| Constraint / action | Evidence / correction |
|---|---|
| ________ | ________ |
| ________ | ________ |
| ________ | ________ |
| ________ | ________ |