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Zap!: What Happens When Static Electricity is Discharged?

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Author: Janice VanCleave

Problem

What happens when static electricity is discharged?

Materials

  • scissors
  • ruler
  • plastic report folder
  • modeling clay
  • large paper clip
  • wool scarf

Procedure

  1. Cut a 2-inch × 8-inch (5-cm × 20-cm) strip from the plastic report folder.
  2. Use a walnut-sized piece of clay to stand the paper clip upright on a table.
  3. Darken the room and wrap the scarf around the plastic strip.
  4. Quickly pull the plastic through the scarf. Do this rapidly at least three times.
  5. Immediately hold the plastic near, but not touching, the top of the paper clip.

Results

A bright spark of light leaps between the plastic strip and the paper clip.

Zap!

Why?

Like all atoms, the atoms in the paper clip have a positive center, the nucleus, with negatively-charged electrons spinning around it. Rubbing the plastic against the wool causes some electrons from the wool to collect on the plastic. This build-up of electrons produces what is called static electricity. These static charges follow the law of electric charges, which states that like charges repel each other and unlike charges attract each other. Holding the negatively charged plastic near the electrically neutral paper clip causes the negatively charged electrons in the clip to move away because of the repulsion between like charges. This creates a positive charge on the surface of the clip near the plastic.

When the charge on the plastic is great enough, the air between the two materials also becomes charged, thereby forming a path through which electrons can move. The resulting spark is called a static discharge, which is a loss of static electricity. This discharge can be a very slow, quiet transfer of charges or, as in this experiment, quick with a spark of light and/or a crackle of sound.

Let's Explore

  1. Does the number of strokes of the wool against the plastic affect the results? Repeat the experiment twice, first rubbing the plastic once, and then rubbing the plastic six times.
  2. Does the material being charged affect the results? Repeat the original experiment, replacing the plastic strip with materials such as a clean drinking glass and a rubber comb.

Show Time!

  1. Lightning is one of the most spectacular displays of static discharge. All of the processes that lead to separation of positive and negative charges in a cloud are not fully understood. Some processes that cause charge separation are the splitting of water drops, the freezing of water or melting of ice, and the rubbing of materials together. During a thunderstorm, violent air currents move up and down inside the clouds, rubbing water droplets and ice crystals against each other. This movement is but one of the processes that fills the clouds with a charge of static electricity—just as rubbing the plastic and wool together in the original experiment produced a charge.
  2. Find out how the discharge of static charges produces lightning between two clouds and between a cloud and the ground. Use this information to prepare a display chart of the events leading up to a flash. Include steps such as:

    • the location of charges in a cloud
    • the movement of a "stepped leader"
    • upward streams of positive charges
    • a stroke of lightning

    Zap!

    For more information about lightning, see pages 126–127 in USA Today: The Weather Book, by Jack Williams (New York: Vantage Books, 1992).

  3.  
    1. Demonstrate that the discharge of static electricity produces radio waves (energy waves that can travel at the speed of light in a vacuum). This can be done by tuning an AM radio to a position between stations and setting a very low volume. Charge an inflated balloon by rubbing it quickly across a piece of wool about 10 times (or rub the balloon against your clean, dry, oil-free hair). As you hold the balloon near, but not touching, the radio antenna, listen for a single pop that will be heard as the static electricity is discharged from the balloon. For more information about radio waves produced by static discharge, see page 180, "Micro-Bolt," in Janice VanCleave's Earth Science for Every Kid, by Janice VanCleave (New York: Wiley, 1991).
    2. To see an example of electromagnetic radiation, repeat the previous experiment, this time holding the charged balloon near, but not touching, a paper clip as in the diagram. This works best in a darkened room. The spark of light is a type of electromagnetic radiation.

Zap!

Check it Out!

According to information found on pages 111–114 in The Weather Companion, by Gary Lockhart (New York: Wiley, 1988), lightning is not equally attracted to all trees. Use this book and other resources to discover which trees are more likely to be struck by lightning. What are the characteristics of trees that are more electrically attractive?

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