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Introduction

The goal of this tutorial is to give the basic background one needs to start analyzing electrical circuit. This will be part 1 of a much bigger tutorial that will show how to do electrical circuit analysis. In part 1, I will be laying down the basic foundation one needs before they can start analyzing electrical circuits. I will assume one have some knowledge of the structure and the working of atom and one knows algebra. But note that to truly understand and electrical circuits one need a background in both trigonometry and calculus but for the first couple of tutorial algebra will suffice. When it comes time that one needs to know more advance math to continue with circuit analysis, I will spin off tutorial on these subjects. Note, I am assuming that you know the protons in the nucleus of an atom are positive and the electrons orbiting the nucleus of an atom is negative. Also, like charges repel while different charges attract.

Coulombs Law

It is common knowledge that like charges will repel each other and unlike charges will attract each other. One gets a feel for this from playing with magnets. The south pole will repel the south pole of other magnets while if one to put the south pole toward the north pole of another magnet, they will attract. Electric charges act the same way. Two negative charge particles will repel while one negative charge particle will attract another positive charge particle. Later you will find that magnetism and electricity are two faces of the same force but this is not that important at the moment. How does one know the amount of force exist between to charge particles? One can find out the force that exists between two charge particles by using Coulomb’s Law which is listed below.

F = kQ1Q2/ r2
F= the force in Newtons
K=constant which is 9.0 X 109
Q1, Q2 = charge of each particle in Coulombs
r = distances in meters between the two particles

Example problem:

Find the force of attraction between two unlike charged particles where Q1=5 X 10-5 C, Q2 = 6 X 10-4 C and the distances between the two particles is 3 m.
F=(9.0 X 109 *5 X 10-5 * 6 X 10-4 )/32 
F= 30 N

Voltage

To understand voltage, one must first understand the definition of Energy. Energy is the capacity to do work. One type of energy a person probably learned in basic physic class is potential energy, which means that it has the potential to do work under the right conditions. One way to think of potential energy is to imagine that a person has a water hose and is blocking water from coming out by placing their thumb over the hose end. That person will be able to feel the pressure pushing against their thumb but as long as they keep their thumb there is no work being done, thus it has the potential to do work but the condition is not there to allow the water to flow and do work. If the person go and open the faucet even more, one would feel the pressure increasing against their thumb. Thus, the potential energy of the water pressure has gone up. Voltage works in much the same way. If one had a battery and is not connected to anything, it has the potential to do work but it is not connect to any circuit so it cannot do any work. The higher the voltage of the battery the more potential energy it has.

Definition of Voltage

Voltage is defined by the amount of energy divided by the charge between two points. The equation is listed below.

V = W / Q
V=voltage between two points
W = amount of energy.  1 joules of energy is defined as the amount of energy to move one 1 coulombs of charge between two points.
C=the charge between two points.

Example Problem

Find the voltage between two points if it takes 80 J of energy to move 20 C of charge between the two points.
V = W/Q = 80/20 = 4 V

Ampere

Ampere is the kinetic energy of the electrical world. It is the capacity to do work due to the movement of an eletrons. Going back to the water hose example, if the person removes his thumb from the hose end and the water flows, the potential energy is converted to kinetic energy. The moving water can perform work. For example the flowing water can wash the dirty off the person’s car. But for the water to be able to flow it must have the potential energy driving it. In the water hose example, it is water pressure. In electrical system, the voltage and ampere works together to drive the circuits.

Definition of Ampere

Ampere is defined as the amount of charge particles that passes a certain point over a period of time. The following formula defines Ampere.

I (Ampere) = Q(Coulombs)/t (seconds)

Example Problem

How many Ampere are there if 20 C of charge passes a point in 10 seconds?
I = Q/t = 20 C/ 10 s = 2 A

Direct Current

Direct Current is when there is a uniform flow of current in one direction. A Direct Current voltage supply is a device that causes the current to flow in one direction. An example that everyone is familiar with is the common battery. Note, the electrical wiring in your house is not a direct current supply; it is an AC (alternate current) supply as the flow of electrons changes direction with the respect to time. AC circuits will be explained in more details in later tutorial. At the moment the focus will be on DC supplies.

Conductors and Insulators

Conductors are materials that allow the free flow of electrons through it. Such items like metals make great conductor and are used to transport electrical power from one location to another. Below is a list of some common conductors and their relative conductivity.

----------------------------------------------------------------
Metals             Relative Conductivity (%)
----------------------------------------------------------------
Silver			105
Cooper			100
Gold			70.5
Aluminum		61
Tungsten		31.2
Nickel			22.1
Iron			14
----------------------------------------------------------------	

Insulators are materials that resist free flow of electrons and it takes a very high voltage to produce any current flow. Below are some common insulators and the average breakdown strength (KV/cm).

----------------------------------------------------------------------
Material		Average Breakdown Strength
----------------------------------------------------------------------
Air				30
Porcelain			70
Oils				140
Rubber				150
Teflon				600
Glass				900
---------------------------------------------------------------------		

Myth Busters: I want to dispel a myth that I hear all the time which makes me nauseous every time I hear it. When lightning strikes a car it is not the rubber of the tires that protects you from getting shocked. It is that the electron flow around the frame of the car which makes you safe. It is called the “skin effect”. Tesla showed this in an experiment where he stood in the middle of a metal ball and struck the ball with bolts of electricity from his tesla coils that he built. He was unharmed because the electron followed the least path of resistance which is along the metal frame. Even though rubber is a better insulator then air, one must think of the thickness of the insulator. The thickness of the rubber is very small compared to the thickness of air the lightning bolt had to travel to hit your car. If lightning has little trouble traveling thousands of feet through the air, it will have no trouble penetrating the small thickness of a tires. Just some food for thought.

Semiconductors

I will not go into much detail about semiconductors at the moment, as this is a tutorial in itself but I will cover it in mind numbing details in later tutorial. At the moment, I just want one to beware of them and know on a basic level what they are. They are not conductors or insulators but whether lay in the middle. When voltage is applied in the right way they will behave like conductors and if voltage is applied in a different way they will act like an insulator. This behavior makes them idea for acting like a switch for turning electron flow on and off. Some common semiconductors that you might be familiar with are transistors and diodes.

Conclusion

This tutorial is the first part of a much bigger tutorial that I will be writing on this site. This first tutorial is to give a person the foundation they need to start analyzing electrical circuits. In the coming weeks I will be adding to this tutorial.

electrical_engineering


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