transfer of electric charge

polarization

Assume that you have walked across a wool carpet in rubber-soled shoes and become negatively charged. If you then reach out to touch a metal doorknob, electrons in the neutral metal will be repelled and move away from your hand before you even touch the knob. In this way, one end of the doorknob becomes positively charged and the other end becomes negatively charged. This is called polarization. Polarization occurs whenever electrons within a neutral object move because of the electric field of a nearby charged object. It occurs without direct contact between the two objects. The Figure 1.2 models how polarization occurs. Q: What happens when the negatively charged plastic rod in the diagram is placed close to the neutral metal plate? A: Electrons in the plate are repelled by the positive charges in the rod. The electrons move away from the rod, causing one side of the plate to become positively charged and the other side to become negatively charged.

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conduction

The transfer of electrons from the van de Graaff generator to the man is an example of conduction. Conduction occurs when there is direct contact between materials that differ in their ability to give up or accept electrons. A van de Graff generator produces a negative charge on its dome, so it tends to give up electrons. Human hands are positively charged, so they tend to accept electrons. Therefore, electrons flow from the dome to the mans hand when they are in contact. You dont need a van de Graaff generator for conduction to take place. It may occur when you walk across a wool carpet in rubber-soled shoes. Wool tends to give up electrons and rubber tends to accept them. Therefore, the carpet transfers electrons to your shoes each time you put down your foot. The transfer of electrons results in you becoming negatively charged and the carpet becoming positively charged.

conservation of charge

Like the formation of ions, the formation of charged matter in general depends on the transfer of electrons, either between two materials or within a material. Three ways this can occur are referred to as conduction, polarization, and friction. All three ways are described below. However, regardless of how electrons are transferred, the total charge always remains the same. Electrons move, but they arent destroyed. This is the law of conservation of charge.

friction

Did you ever rub an inflated balloon against your hair? You can see what happens in the Figure 1.3. Friction between the balloon and hair cause electrons from the hair to rub off on the balloon. Thats because a balloon attracts electrons more strongly than hair does. After the transfer of electrons, the balloon becomes negatively charged and the hair becomes positively charged. The individual hairs push away from each other and stand on end because like charges repel each other. The balloon and the hair attract each other because opposite charges attract. Electrons are transferred in this way whenever there is friction between materials that differ in their ability to give up or accept electrons. Q: If you rub a balloon against a wall, it may stick to the wall. Explain why.

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transferring electrons

The girl pictured above became negatively charged because electrons flowed from the van de Graaff generator to her. Whenever electrons are transferred between objects, neutral matter becomes charged. This occurs even with individual atoms. Atoms are neutral in electric charge because they have the same number of negative electrons as positive protons. However, if atoms lose or gain electrons, they become charged particles called ions. You can see how this happens in the Figure 1.1. When an atom loses electrons, it becomes a positively charged ion, or cation. When an atom gains electrons, it becomes a negative charged ion, or anion.

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instructional diagrams

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questions

all atoms are neutral in electric charge.

-->  a. true

b. false

the formation of charged matter always depends on the transfer of electrons.

-->  a. true

b. false

ways that matter can become electrically charged include

-->  a) conduction.

b) convection.

c) radiation.

d) all of the above

conduction occurs when you

-->  a) touch a van de graaff generator.

b) rub a balloon on your hair.

c) reach toward a metal doorknob.

d) two of the above.

polarization occurs only when there is direct contact between two objects.

a. true

-->  b. false

electrons are transferred whenever there is friction between materials that differ in their ability to give up or accept electrons.

-->  a. true

b. false

diagram questions

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