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Lesson_2.1_Printable_PPT

Lesson_2.1_Printable_PPT - Electric Charge Electricity is...

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Electric Charge Protons which are found in the core of an atom carry a positive electric charge ( e ) and they are fixed to their relative positions. Electricity is fundamental to nature. Atoms, which are the basic constituents of matter are made up of electrically charged particles. Electrons are found moving in the space surrounding the core of the atom and they carry an equal amount of negative electric charge (-e )
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e is the fundamental unit of charge. This means that the charge carried by anything else comes in multiples of e. A proton and an electron together form a neutral object with no net electric charge. This means that a neutral object contains equal quantities of positive and negative charges. Electric charge is measured in a unit called coulomb (C). This is a large unit and is divided into mC (10 -3 C), μ C (10 -6 C), nC (10 -9 C) and so on. e = 1.602 × 10 -19 C .
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Example 1: A charge equal to the charge of Avogadro’s number (6.02 x 10 23 ) of protons is called a faraday. Calculate the number of coulombs in a faraday. The charge of one proton e = 1.602 × 10 -19 C. The charge of 6.02 × 10 23 protons is: 6.02 × 10 23 × 1.602 × 10 -19 C. = 96440 C
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The atomic mass of copper is 63.5 g Example 2: How many coulombs of negative charge are there in one gram of copper? This means that the mass of one mole of copper = 63.5 g One mole of copper contains Avogadro’s number (6.02 × 10 23 ) of atoms. Therefore, the number of atoms in one gram of copper is: = 9.48 × 10 21 23 6.02 10 63.5 N × =
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N = 9.48 × 10 21 Each atom in copper carries 29 electrons. Total number of electrons in one gram of copper = 9.48 × 10 21 × 29 = 2.7 × 10 23 The total charge carried by 1 g of copper = 2.7 × 10 23 × 1.602 × 10 -19 = 43254 C
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While protons are fixed to their relative positions in a material, electrons are free to move. Conductors and Insulators In some materials, especially metals, electrons that are relatively at large distances from the core of the atom are very loosely bound to the atom and they are virtually free to move about in the material http://www.ndt- ed.org/EducationResources/HighSchool/Electricity/ conductorsinsulators.htm
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If there is some excess charge on this material, it will spread all over the material because it allows charges to move through. Such materials are called conductors. Most metals are considered to be good conductors In some other materials, electrons are localized and are not allowed to move from one part of the material to another. Such materials do not allow electric charges to flow through them and are called insulators . Both conductors and insulators play vital roles in building electrical circuits.
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Interaction between electric charges. 1. Like charges repel. Two positive charges placed together will move away from each other. Similarly two negative charges will move away from each other. The fundamental properties of electric charges are: 2. Unlike charges attract. A positive charge and a negative charge will move towards each other because of the attraction they have for each other
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An electroscope like the one shown on the left can be used to detect the presence of an excess charge.
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