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Lightning!

Classroom Activity

Objective
To observe the spark effect of static electricity.

• copy of "Indoor Lightning" student handout (PDF or HTML)

• A piece of notebook paper or a sheet of plastic, such as a transparency sheet

• Two or three flat pieces of metal, such as a 12" x 12" square of aluminum foil folded into a flat disc, the top of a metal can, or the bottom of an aluminum pie pan (Be careful with sharp edges.)

• A piece of wool cloth (mittens or pieces of a sweater work well)

• A stopwatch or a clock with a second hand

1. A lightning bolt is an enormous release of static electric charge. We commonly experience the phenomenon of small amounts of static electricity when removing clothes from the dryer, brushing our hair, or walking across a carpeted floor and then touching a metal doorknob. Most of the time the sparks from these static electric releases are not visible, so the connection between these experiences and lightning may not be evident to students.

2. To demonstrate the spark effect of static electricity, have students try this activity. (This activity will be most successful on a very dry day or in winter.)

3. Organize the students into pairs and give a set of materials to each team. If possible, darken the room to make the sparks more visible. Point out to the class that it takes a lot of physical energy to create enough of a charge to make a small, barely visible spark. This energy is insignificant compared to the amount of electric charge that builds up in a thundercloud.

4. After the students complete the activity, challenge them to relate each phase of the activity to the equivalent atmospheric phase in the formation of a lightning bolt.

When students rub the wool piece on the paper, they build up a negative electric charge on the paper. The metal sheet also carries a negative charge. This negative charge is increased when the metal is placed on the paper. When the students' fingers touch the metal, the negative charge is attracted to the positive charge in their bodies and creates a spark. Lightning is formed in a similar manner. Under normal atmospheric conditions, the electrical charge of the ground is evenly balanced between positive and negative. The most frequent type of lightning occurs when a thundercloud has built up a strong negative charge. It repels the negative charge of the ground, causing the charge to be pushed down slightly, similar to the effect of holding two magnets so that their like charges repel each other. With the negative charge pushed down, the ground becomes more positively charged, creating an attractive force for the negative charge in the thundercloud. This same effect also occurs when students place the negatively charged metal on top of the negatively charged paper and then place their positively charged fingers near the negative charge.