Passive Optical Schlieren Heat-Wave Shadowgraph

30 mins Ages 10-14 Indoor

A challenging, hands-on discovery and STEM project designed for curious young minds aged 10 to 14.

Materials Needed

  • • Smartphone LED light or bright single-die LED penlight (1 unit)
  • • Aluminum foil and pin (to create 1 mm pinhole aperture) (1 piece)
  • • Heat source (hair dryer, warm clothes iron, or toaster) (1 unit)
  • • Blank white wall in a fully darkenable room (1 room)

Pro Tips

  • → Place a single-point LED light source (cover a phone flash with foil with a tiny pinhole) 3–4 meters away from a smooth white wall in a dark room.
  • → Hold a hot object (hair dryer, warm iron, or hands) in the light path about 30 cm from the wall.
  • → Warm air has a lower refractive index than cool air, bending light rays to cast flowing shadow waves of rising air currents onto the wall.

Safety First

Do not touch hot hair dryer nozzles or toaster heating elements.

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Step-by-Step Instructions

1

Step 1

Cover a smartphone flashlight with foil and poke a 1 mm pinhole to create a bright single-point light source.

2

Step 2

Darken the room and set the light source 3 meters away from a blank, smooth white wall.

3

Step 3

Hold a warm hair dryer or hot mug of water 30 cm in front of the wall directly in the light beam.

4

Step 4

Look at the wall to see the shadowgraph: rising turbulent plumes of heated air cast moving ripples across the surface.

What they are learning

Shadowgraphy refractive index gradient mapping Thermal convection density variations Invisible fluid flow optical visualization