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Black Light Bubbles

In this investigation, students add a phosphor to soap mix to make some fluorescent bubbles.

A black light gives off harmless, highly energetic, ultraviolet (UV) light that is invisible to humans. Certain fluorescent substances absorb ultraviolet light and re-emit it at a different wavelength, making the light visible and the material appear to glow.

What you see glowing under a black light are phosphors. A phosphor is any substance that emits visible light in response to some sort of radiation. Here, light is the form of radiation.

UV light makes certain objects glow because the objects contain "phosphors" which absorb the energy from UV light then release it again as visible light.

Objectives

  • Discuss why black light makes phosphors glow.

  • Create glowing bubbles for hands on creativity.

Materials

  • Per Demo or Student Group (for older students):
    Steak knife
    Cutting board
    Neon highlighters or washable fluorescent paint
    Liquid dishwashing detergent
    Water
    Glycerine
    Bubble wands
    Small containers

Key Questions

  • Why does the highlighter ink allow the bubbles to glow under the black light?

What To Do

Preparation
Make the two solutions:

Soap Solution
Mix 1 part liquid dishwashing detergent, 15 parts water and 0.25 parts glycerine.

Glow Solution
Cut open a yellow or orange highlighter using a sharp knife and remove the ink soaked felt. Soak it in a small amount of water for a few minutes, then squeeze the felt into the water to extract more ink.

Note: premixed bubble solution and fluorescent paint can be used.

Instructions

  1. Mix your glow and soap solution in about a 50:50 ratio. You can adjust this ratio depending on how well your bubbles form/glow under the black light.
  2. Dip your bubble wands into the new glowing solution and blow bubbles
  3. Turn out the regular lights and use black light to see the bubbles glow in the dark.

Extensions

  • Use phosphorescent paint instead. You’ll have to shine bright light on your bubble solution; then you can turn off the lights and make bubbles that glow in the dark.