{"id":115,"date":"2017-09-04T04:31:47","date_gmt":"2017-09-04T04:31:47","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/general-science\/?page_id=115"},"modified":"2017-09-21T13:47:32","modified_gmt":"2017-09-21T13:47:32","slug":"electricity","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/general-science\/electricity\/","title":{"rendered":"Electricity"},"content":{"rendered":"
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\u2b05 Previous Lesson<\/a>\u00a0Workshop Index<\/a>\u00a0Next Lesson \u27a1<\/a><\/div>\n

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Electricity<\/h1>\n
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Electrostatics<\/h3>\n

What is the reason for the warnings printed on gas pumps cautioning us not to get in and out of the car when we\u2019re pumping gas? The reason is that cars pick up electrostatic charges as they run, and the car\u2019s tires insulate that charge from the ground. Electrostatics<\/abbr> is the study of electrical charges on objects at rest.<\/p>\n

There are two fundamental charges: positive and negative. We know that similarly charged objects repel and oppositely charged objects attract. Besides this, objects that are neutral (i.e. objects with an equal amount of positive and negative charge) are attracted to both positive and negative objects. Why do we know this? Let\u2019s first review the basic model of the atom.<\/p>\n

The very center of the atom is a tiny concentrated region that contains positive particles (protons) and neutral particles (neutrons), called the nucleus. The number of protons in the nucleus uniquely determines what element it is. This number will not change unless a \u201cdrastic\u201d nuclear event occurs (i.e. fission or fusion). In the large region of space around the tiny nucleus there is likelihood that you will find negative particles (electrons). In neutral atoms, the number of electrons equals the number of protons. In order for an object to gain a negative electric charge, it gains extra electrons. To pick up a positive charge, the object loses electrons. Thus, electrons are the \u201cmobile fluid\u201d responsible for charging objects. An object will always<\/em> have the same amount of protons before and after gaining an electrostatic charge.<\/p>\n

Some elements are naturally good conductors of electricity. Conductors<\/abbr> are materials in which electrons flow easily from atom to atom. Metals are excellent examples of conductors. Dielectrics<\/abbr>, or insulators, are materials in which the electrons are tightly bound to a particular nucleus. Rubber, plastic, and air are examples of good insulators. Under conditions with very high voltages, even insulators may have electrons travel throughout the material.<\/p>\n

Why are neutral conductors and neutral insulators attracted to charged objects? The explanation is a little different for each. When a negatively charged object is brought near a conductor, the electrons in the conductor are repelled by the electrons in the charged object. The free electrons in the rod are forced to move to the opposite side of the rod, leaving the positive nuclei to attract the negative object. This process is called electric induction and is represented in the following diagram:<\/p>\n

\"Electric<\/center>In contrast, when a charged object is brought near a dielectric (insulator), the electrons will not move to the one side of the entire object. Rather, the electrons tend move within the atom such that the atoms are polarized. For example, if a negative balloon is brought near a wall, electrons in the atom of the wall are repelled to the opposite side of the nucleus. This leaves the positive nucleus in close proximity to the negative object and they attract one another. This process of polarization is represented in the following diagram:<\/p>\n

\"Electric<\/center><\/p>\n
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Question<\/h4>\n

In an electrostatics experiment, two pieces of tape attract each other. The most\u00a0<\/b>you can\u00a0conclude is that:<\/p>\n

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  1. at least one of the pieces of tape must be charged.<\/li>\n
  2. both pieces of tape must be negatively charged<\/li>\n
  3. both pieces of tape must be oppositely charged.<\/li>\n
  4. you did the experiment incorrectly.<\/li>\n<\/ol>\n

    Reveal Answer <\/a><\/p>\n

    The correct answer is A. It is tempting to answer C because we know that oppositely charged objects attract, but that is not the only case in which we observe an attraction. Neutral objects also attract charged objects, so all we can confidently conclude in this question is that at least one of the pieces of tape is charged. The other piece of tape could be neutral or oppositely charged.<\/p>\n<\/section>\n

    Electric Fields<\/h3>\n

    In the vicinity of charged objects, there exists an electric field in which other charged objects will experience forces. The charged objects have \u201clines of force\u201d or \u201cflux lines\u201d emanating from them. The direction of the force exerted on a positive test charge placed near a charged object is shown by placing arrowheads pointing into the object to represent a negatively charged body, or arrowheads pointing out of the object if it is a positively charged body. For example, the first diagram below shows that a positive test charge is repelled from a positive central charge (+Q). The second diagram shows that the same positive test charge is attracted to a negative central charge (-Q).<\/p>\n

    \"Positive<\/center>Mod5Fig23s<\/p>\n

    <\/center><\/p>\n