StaticElectricity

# Figure 1 cross section of an atomic model of an

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Figure 1 Cross section of an atomic model of an insulating material. The negatively charged electrons are tightly bound to their host nuclei, and thus cannot move around freely throughout the material. We say then that these materials do not conduct electricity well. In contrast, an atomic model of a conducting material is shown in Figure 2. Again, if the material is neutral, there must be equal numbers of positive and negative charges. Here, though, not all of the negatively charged electrons are completely bound to their nuclei. The outermost electrons, typically called the valence electrons , are free to wander anywhere throughout the solid. They continually bounce about the solid randomly, and they can very easily and rapidly redistribute themselves if external (or internal) conditions change. Figure 2 Cross section of an atomic model of a conducting metal. The electrons are not tightly bound to their nuclei and thus bounce randomly throughout the metal much like the atoms of a gas or liquid. We often refer to these e lectrons as a “sea of electrons” to remind us of how easily they can flow through the metal. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

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Static Electricity Name: ____________________________ Sect.: _______ Name: ____________________________ Name: ____________________________ Directions: Note : If you are not careful while handling the materials in the activity, you may obtain inconsistent results. Please follow the directions as faithfully as possible! The following experiments will need you to use strips of tape that are about 20 cm long. Each time you are asked to use a strip of tape, fold over one end to form a non-sticky handle for easy handling, as in Figure 3. Figure 3 Preparing a strip of tape by making a non-stick handle Activity 1: Examining a “T” strip Stick a 20-cm strip of tape on the lab table, sticky side down. This tape forms a standard base for making a “T” (for “ T op”) strip. Stick another strip of tape on top of this one, smoothing it down well with your thumb and fingers. Using a pen or marker, label the handle of this strip with a T ”. With a quick motion, peel off the T-strip from the base strip. Test whether this T-strip is attracted to your finger (but do not let it touch your finger). If the strip is not attracted to your finger, repeat the steps above. Once you know how to make a T-strip, prepare two such strips. Holding each one by the handle, bring the slick (non-sticky) sides of the two strips toward each other. Observe what happens, noting how the behavior changes with the distance between the strips. Q1. Describe and explain what happens as the two T-strips are brought closer together. Q2. What qualitative conclusions can you draw about the relationship between electric force and the distance between charged objects? How do your obs ervations relate to Coulomb’s Law?

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Static Electricity Q3. Can you tell from your experiment so far whether the T-strips carry a positive charge or a negative charge? Briefly explain your answer.
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