To understand why this is the case, you have to understand more about the nature and structure of atoms. In this section, we discuss how and why electric charges do—or do not—move through materials Figure 1.
A more complete description is given in a later chapter. Figure 1. As discussed in the previous section, electrons surround the tiny nucleus in the form of a comparatively vast cloud of negative charge. However, this cloud does have a definite structure to it. It can be easily dislodged; it then moves to a neighboring atom. In a large mass of copper atoms such as a copper wire or a sheet of copper , these vast numbers of outermost electrons one per atom wander from atom to atom, and are the electrons that do the moving when electricity flows.
All conducting elements have a similar arrangement of their electrons, with one or two conduction electrons. This includes most metals. Insulators , in contrast, are made from materials that lack conduction electrons; charge flows only with great difficulty, if at all. Even if excess charge is added to an insulating material, it cannot move, remaining indefinitely in place.
This is why insulating materials exhibit the electrical attraction and repulsion forces described earlier, whereas conductors do not; any excess charge placed on a conductor would instantly flow away due to mutual repulsion from existing charges , leaving no excess charge around to create forces.
Charge cannot flow along or through an insulator , so its electric forces remain for long periods of time. Charge will dissipate from an insulator, given enough time. As it happens, amber, fur, and most semi-precious gems are insulators, as are materials like wood, glass, and plastic.
It is not possible to predict in advance which way the electrons will be transferred for a certain material. The same cloth , when rubbed against a different type of plastic called acetate , will gain electrons and become negatively charged, leaving the acetate with a positive charge.
Links Electrostatic Charge Revision Questions. All Rights Reserved. Polar molecules have a natural or inherent separation of charge, although they are neutral overall.
Polar molecules are particularly affected by other charged objects and show greater polarization effects than molecules with naturally uniform charge distributions.
Water molecules are polarized, giving them slightly positive and slightly negative sides. As the water flows downward, due to the force of gravity, the charged conductor exerts a net attraction to the opposite charges in the stream of water, pulling it closer.
Make sparks fly with John Travoltage. Bring his hand close to the door knob and get rid of the excess charge. Skip to main content. Electric Charge and Electric Field. Search for:. Conductors and Insulators Learning Objectives By the end of this section, you will be able to: Define conductor and insulator, explain the difference, and give examples of each.
Describe three methods for charging an object. Explain what happens to an electric force as you move farther from the source. Define polarization. Check Your Understanding Can you explain the attraction of water to the charged rod in Figure 6? Figure 6. Click to run the simulation.
Conceptual Questions An eccentric inventor attempts to levitate by first placing a large negative charge on himself and then putting a large positive charge on the ceiling of his workshop. Instead, while attempting to place a large negative charge on himself, his clothes fly off.
If you have charged an electroscope by contact with a positively charged object, describe how you could use it to determine the charge of other objects. Specifically, what would the leaves of the electroscope do if other charged objects were brought near its knob? When a glass rod is rubbed with silk, it becomes positive and the silk becomes negative—yet both attract dust.
Does the dust have a third type of charge that is attracted to both positive and negative? Why does a car always attract dust right after it is polished? Note that car wax and car tires are insulators. Describe how a positively charged object can be used to give another object a negative charge. What is the name of this process? What is grounding? What effect does it have on a charged conductor?
On a charged insulator? How many electrons does it have? An amoeba has 1. Each copper atom has 29 protons, and copper has an atomic mass of
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