Basic Electricity

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EAS 199A Lecture Notes: Basic Electricity

Fall 2011

This course module introduces the basic physical models by which we explain the flow of electricity. The Bohr model of an atom – a nucleus surrounded by shells of electrons traveling in discrete orbits – is presented. Electrical current is described as a flow of electrons. Ohm’s law – the relationship between voltage, current and electrical resistance – is introduced. Learning Objectives Understanding the basic principles of electricity is a foundational skill for all branches of engineering. Understanding electricity is required to use electrical sensors, switches, digital and analog devices, and microcontrollers. In this course, students will use breadboards to assemble electronic components for reading data from sensors and controlling switches, lights, motors and other actuators. The larger purpose is to learn how to incorporate electronic components into solutions to engineering design problems. Successful completion of this module will enable students to 1. Link basic model of an atom to the flow of electricity; 2. Understand the definition of fundamental quantities related to the flow of electricity: coulomb, amp, volt, ohm, joule and watt; 3. Apply Ohm’s Law to single electronic components and to simple circuits. Definition of Electricity and Electrical Charge According to the Concise Oxford English Dictionary, revised 10th edition, the first definition of electricity is a form of energy resulting from the existence of charged particles (such as electrons or protons), either statically as an accumulation of charge or dynamically as a current.

Thus, to describe electricity we must introduce the idea of positive and negative electrical charge, which is stored energy associated with particles – electrons and protons. It is tempting to think of electrons and protons as discrete, hard objects, like marbles. However, the physical reality is much more complicated. Electrons are highly mobile concentrations of energy that hold the negative charge. Electrons moving around an atomic nucleus can only occupy discrete or quantized energy levels. Those levels are called electron shells. Protons are themselves composed of subatomic particles that give the entity called a proton its mass and charge. We will use a somewhat crude and simple model of atoms, protons and electrons that allow us to develop a practical understanding of electricity. It is important to understand that this simple model is just that, a model, not a precisely accurate representation of the complex physical world. We will avoid the temptation get lost in the fascinating and bewildering realm of atomic and subatomic physics. When the arrangement or distribution of electrical charge does not change, it is called static charge or static electricity. The build-up of electrical charge creates the potential for the flow of electricity. When that flow is prevented, static charge accumulates. When you scuff your stocking feet across a synthetic carpet, you store charge on the surface of our body. The charge may cause the hairs on your body to prickle, or in extreme cases, stand on end. When the accumulated charge is suddenly released, for example, when you touch a light switch or other grounded metal object, you feel a shock as the electrical current surges between your body and the grounding object. The shock is the sudden release or discharge of the static electricity.

EAS 199A: Basic Electricity

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Similarly, lightning is the discharge of large amounts of charge accumulated in clouds during storms. Static electricity is important, at least because the build-up of static charge can cause problems when that charge is released. However, much of modern technology is possible because of the controlled flow of electricity, i.e. the movement of charge between regions of positive and negative charge. Conductors, Insulators and Semiconductors Materials can be classified as conductors, insulators, and...
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