Flashers!: What Causes Lightning?

Problem

What causes lightning?

Materials

• Duct tape
• Helper

Procedure

1. Unroll about 4 inches (5 cm) of the tape from the roll, but do not cut the strip of tape.
2. Hold the roll of tape in one hand and the end of the tape in the other hand.
3. Position the roll of tape so that you are looking at the place where the tape is being pulled from the roll.
4. Ask a helper to turn off the lights in the room. The best results will occur in a completely darkened room.
5. Jerk the end of the tape several times so that more tape is unrolled very quickly.

Results

Flashes of light appear across the area where the tape is pulled from the roll.

Why?

Matter is anything that takes up space and has weight. All matter is made of tiny units called atoms. An atom is the smallest part of an element that retains the properties of that element. Atoms are made of smaller units called protons and electrons. There are only two known types of electric charges, positive and negative. A proton has a positive electric charge and an electron has a negative electric charge. Protons are located in the center or nucleus of the atom, and electrons are located around the outside of the nucleus. Each atom usually has the same number of electrons and protons; however, electrons can become separated from atoms. A separation of charges occurs in this experiment when the tape is quickly jerked from the roll. The sticky part of the tape and the surface of the tape still attached to the roll are each left with an excess electric charge; one has an excess positive charge and the other has an excess negative charge. The buildup of excess electric charges in one place is called static electricity.

The law of electric charges states that unlike charges attract each other and like charges repel each other. Electrons are able to move from one material to the other. The attraction between the positive and negative charges causes the movement of electrons between the two charged surfaces. This movement is called static discharge, which is a transfer of static electricity. This static discharge energizes the atoms of the gases in the air, causing a spark of light.

Lightning is just a larger flash of light due to static discharge in the atmosphere. lightning occurs when charges separate within a cloud, making the bottom of the cloud more negatively charged than the top of the cloud. The negative charges in the bottom of the cloud repel the negative charges in the neutral atoms (atoms with the same number of positive and negative charges) in the ground or other structures directly beneath the cloud. Thus, the ground becomes positively charged because of the buildup of positive charges at the ground's surface. The electrons in the clouds move to the ground. This happens when the attraction between the negative charges in the cloud and the positive charges in the ground becomes great enough to overcome the air's resistance to electrical flow.

Let's Explore

1. Does it matter how quickly the tape is separated from the roll? Repeat the experiment twice. The first time, gently pull the tape off the roll. The second time, jerk the tape with more force than in the original experiment.
2. Would tape made from other materials affect the results? Repeat the original experiment using different kinds of tape, such as masking tape, electrical tape, and transparent tape.

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