This model uses a point source, an opaque object and a fixed screen. Rays passing the object's edges define the shadow. Similar triangles connect object height and distance with shadow height and distance. Changing the object's position changes the magnification; it does not change the object's real dimensions. The shadow height is object height times source-to-screen distance divided by source-to-object distance.
Light, sound and electricity · Discover & try
What makes a shadow bigger?
Reading level 3 of 5 · IndependentChange
Word help
opaque
Not letting the model light pass through.
ray
A line representing the direction light travels.
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See how it works
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Point-source projection; sharp edges and distances are idealised, not a real lamp measurement.
What to look for
- Edge rays continue straight
- The object keeps its own size
- A closer object makes a wider projection
Explain what you noticed
A fixed screen is 6 units from a point lamp. A 1-unit object moves from 3 units to 2 units from the lamp. What happens?
Keep this idea: A shadow can change size without its object changing size.
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Source material checked 2026-10-28. Explanations and activities by Nepedia. Source links do not imply endorsement.
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