Explore in 3D · Light model

Light in a paper room

A flashlight is a light source: it makes its own light. Put one material in the beam at a time, and watch where the light goes. Slide the cardboard to make its shadow grow and shrink. We see things only when light travels from them into our eyes.

Real flashlights: never shine one into anyone's eyes.

Goes with

The paper room model

A model, not to scale

The flashlight shines on the paper screen. Light bounces off the screen into the eye.

Try this

Real flashlights: never shine one into anyone's eyes.

  1. Turn the flashlight off. Can the eye see anything?

  2. Put each material in the beam, one at a time. Which one makes a shadow?

  3. Put in the Cardboard. Slide it toward the flashlight, or press Play the sweep. Does its shadow get bigger or smaller?

  4. Use the Smooth foil. Where does the bright patch go?

What did you notice?

  • Which material let light pass through?
  • Which one bounced the light?
  • When was the shadow biggest? When were its edges fuzzy?
  • How did the light get to the eye?

Tell a grown-up, or draw it in your workbook.

For grown-ups: what this model shows, and what it changes
  • Not to scale. The room, flashlight and eye are toy-sized. The arrows show where light goes. Real light paths cannot be seen from the side unless dust or mist is in the air.
  • How we see. We see an object only when light from it travels into our eyes. The eye does not send anything out. The model shows the eye seeing a spot only when light from that spot can reach it.
  • Shadow size and fuzzy edges. Moving the cardboard closer to the flashlight makes its shadow bigger. A bigger glowing part makes the shadow edges fuzzier. The model works out the shadow from the size of the glowing part, so the fuzzy edge follows the same rule as a real lamp. The distances are measured in model centimeters. Real flashlights have reflectors and lenses, so their shadows are less tidy.
  • Brightness is a model number. The brightness score only compares one setting with another in this model. It follows the rule that light spreads out and gets dimmer with distance. It is not a light-meter reading.
  • Four materials. Clear plastic is transparent: light passes through. Wax paper is translucent: some light passes but spreads out. Cardboard is opaque: it blocks light and makes a shadow. Smooth foil is shiny: it reflects light to a new place, leaving at the same angle it arrived. The model makes wax paper spread light with a simple glow, not a full model of light inside paper. The bounced patch from the foil is drawn round.
  • Safety, as the workbook says. Use a battery flashlight, not a flame or a laser. Never shine light into anyone’s eyes. Keep room pathways lit. The model will not aim the flashlight at the eye.
  • Real test first. Weeks 17 and 18 test real materials with a real flashlight. Use the model afterward to talk about what happened.