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Light a Bulb with a Balloon

We are used to thinking that it takes a lot of energy to produce light. This time, we will see that even a small amount of the right kind of energy can give us some light.

This experiment will not work with the incandescent bulbs commonly used in lamps. They have a thin wire, called a filament, which has to get hot enough to glow to give you some light. That takes quite a bit of energy, and much of it is lost as heat.

The fluorescent bulb does not have a filament. Instead, the air has been removed and replaced with mercury vapor and other gases at low pressure. When high voltage electricity moves through a gas, it can change the gas into plasma, the fourth state of matter. We have all learned about solids, liquids, and gases, but plasma, the fourth state is by far the most abundant kind of matter in the universe. Plasma is like a gas that has had its electrons ripped away. The atoms are surrounded by a sea of electrons, making plasmas very good conductors of electricity. When you consider that stars (as well as flames, electric sparks, and the glow in a neon light) are made up of plasma, you can see that it is very abundant, making up over 98% of all the known matter in the universe.

You will need:

  • a balloon
  • a fluorescent light bulb
  • a very dark room

Would you like to produce some plasma? Hold the bulb in one hand. Rub the balloon briskly on your hair (or a piece of cloth if you are "hair challenged" as I am.) You can test to see if you are getting a charge by bringing the balloon near the back of your hand. If the hairs on you hand stand up, you have a good charge. If they don't, get out the hair drier and dry the balloon and your hair and try again.

Once you have a good charge, turn out the lights and get the room as dark as is possible. Wait for your eyes to adjust to the dark. Then rub the balloon on your hair and bring the fluorescent bulb close to it. You will see some flashes of light as the static charge from the balloon jumps to the bulb.

The charge from the balloon is enough to rip some of the electrons away from some of the atoms in the mercury vapor. That changes them into plasma, which causes them to give off light. The light that the mercury vapor gives off is ultraviolet light, a color your eyes can't see. That light hits the inside of the glass tube, which is coated with a powder that glows in the presence of ultraviolet light. That glow is the light you get from a fluorescent bulb.