Lesson_2.1 - Lesson 2.1 Electric Charge Lesson Objectives:...

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Lesson 2.1 Electric Charge Lesson Objectives: At the end of this lesson students will be able to describe Coulomb’s law in electrostatics and use it to solve problems. 1. Electric Charge. Electricity is fundamental to nature. Atoms, which are the basic constituents of matter are made up of electrically charged particles. Protons which are found in the core of an atom carry a positive electric charge and they are fixed to their relative positions. Electrons are found in the space surrounding the core of the atom. They carry a negative electric charge and they are free to move about. The charge carried by an electron is the fundamental unit of charge. This means that the charge carried by anything else comes in multiples of e. The charge of a proton is e and that of an electron is –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. The value of the fundamental electric charge is e = 1.602 x 10 -19 C . 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. Solution: The charge of one proton e = 1.602 × 10 -19 C. The charge of 6.02 × 10 23 protons = 6.02 × 10 23 × 1.602 × 10 -19 C. = 96440 C Example 2 : How many coulombs of negative charge are there in one gram of copper?
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Solution: The mass of one mole of copper = 63.5 g. One mole of copper contains Avogadro’s number (6.02 x 10 23 ) of atoms. Therefore, the number of atoms in one gram of copper is: 23 21 6.02 10 9.48 10 63.5 × = × Each atom in copper carries 29 electrons. Total number of electrons in one gram of copper is: 9.48 × 10 21 × 29 = 2.7 × 10 23 . The total charge carried by 1 g of copper is: Q = 2.7 × 10 23 × 6.02 × 10 -19 = 165500 C 2. Conductors and Insulators While protons are fixed to their relative positions in a material, electrons are free to move. 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. 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 . 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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This note was uploaded on 05/01/2011 for the course PHY 2049 taught by Professor George during the Spring '11 term at Edison State College.

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Lesson_2.1 - Lesson 2.1 Electric Charge Lesson Objectives:...

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