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Study guide

Up to date as of January 14, 2010

From Wikiversity

   Welcome to this lesson on Electrical Current.  

In this lesson the flow of electrons, electrical current, is described and characterized in contexts of voltage, resistance, and simple, useful electric components.

Electrical current results when a voltage or electromagnetic force causes movement of electrons. Since electrons need not be bound to atoms, it is important to exclude atoms, conductors, resistors, what have you in our definition of current flow.

   Electrons in, electrons out

The most common mention of current flow concerns the movement of electrons within conductors to supply power to some kind of electrical load.

An electrical or electronic load is something that needs electrical power to operate and uses more than it produces.

   Hot electrons

We have to drop into physics lecture mode for a moment. Temperature is a measure of the energy contained within a substance. Imagine for a moment that you used the Star Trek transporter to take one tiny atom out of a block of granite. That tiny atom was just in the process of bouncing around against its neighbors. It is now liberated. Imagine that it was liberated into a gravityless vacuum. If you were to slow that atom down to a standstill, you would have to add a quantity of energy to it. Right?

Now, imagine doing that for every last single solitary atom contained within that block of granite. You don't care which direction each atom is going; you just care how much energy it would take to stop each dead in its tracks. Got the picture?

Okay, so now we add all of that energy up. All of that THERMAL energy. In other words, thermal energy is the sum total of all the vibrational energy contained in the object's component parts. We could go on and discuss thermal conductivity, BTUs, calories, inertia, and their relationship to temperature but that would be too serious a digression.

   Electron flow excitement

So, when electrons flow through a material, they cause anything from an insignificant quantity to a catastrophic amount of vibrational energy or heat to be created.

   Current carriers

Insulators do not normally allow electron flow. To overcome that effect, voltage would have to be raised tremendously high. For a spark to cross the insulating gap of air between his finger and the office door, the cube farmer would have to build up thousands of volts of static potential. However, there is only the air there to be heated and so it simply has too few bits of matter to support heating. Vacuum, as you already surmised, has only the electrons themselves and only during the course of their passage.

Semiconductors will begin conducting after only a little voltage 'encourages' the flow. Before, it acts like an insulator. After, it acts like a conductor.

Resistors are designed to resist the flow of electrons. They may be of many materials and, in fact, even conductors display the same characteristics, but to a far smaller extent. Resistors are manufactured as identified components in circuitry. Not surprisingly, the filaments in electric lights, electric stove coils, blow dryer elements and space heater coils are also resistors.

Conductors allow electrons to flow quite freely. They do, however, present some resistance to current flow. Thus, you can cause them to heat up by 1) passing more than the designed current or 2) insulating them so that the tiny heat that is normally generated has nowhere to go and builds up to a potentially disastrous temperature.

Superconductors are conductors with the characteristic of passing electrons with negligible heating and resistance. The current state of technology insists that they be cooled to a very low temperature. Should room temperature superconductors ever be created, there would be no power wasted over the (currently resistive) power lines between our power plants, and our cities and towns. That would cut carbon emissions, well, a whole lot.

   Hot and hotter

In a lightbulb, that heat becomes so great that the tungsten filament glows white hot. Stove and blow dryer elements can glow red-hot. A space heater may not glow but it can still burn the dickens out of you if you are not careful. Light generated is directly related to temperature. If two objects give off the same color of light, they share identical temperatures.

Heat, so desirable in a light bulb, can be disastrous in your house wiring or your PC.

   Experimentation in current carriers

Experimentation is used to determine a substance's resistance characteristics with regard to current flow. Experimental results show that increasing the conductor size decreases its resistance proportionately. So, double the cross-section of a wire and you halve its resistance.

The unit of current is the Ampere or Amp for short. It is defined as a specific number of electrons flowing across a specific point per unit time.

   Current, Power and mathematic equations

We have spent a great deal of time talking about current and its thermal effects. Let's consider what we know. When voltage goes up in a circuit, current goes up. If I double the voltage and the resistance remains constant, I double the current. I also double the vibrations I'm causing so I double the amount of heat I am adding. In other words, doubling voltage doubles the power generated in the form of heat. This leads us to an equation. Power equals Current times Voltage. The symbol for Power is P, the symbol for Current is I, and the symbol for voltage is E. We have P = I * E.

As I double the resistance, I halve the current when constant voltage is applied. Resistance and current are inversely related. As I double the voltage, the current doubles as well. In point of fact, Voltage equals Current times Resistance or E = I * R.

   Assignments

Look up the definition of an Amp. Calculate the value of 50 amps in the terms you found. Provide at least three correct answers.

For extra credit, write a paper on Tesla (the inventor, not the band). If you plaegerize Wiki, you will be found out.

  1. Up to EE_99_Principles_of_electricity

Shawn Daniel Hendricks 21:06, 16 May 2007 (UTC)


Wikibooks

Up to date as of January 23, 2010
(Redirected to Electronics article)

From Wikibooks, the open-content textbooks collection


Electronics | Foreword | Basic Electronics | Complex Electronics | Electricity | Machines | History of Electronics | Appendix | edit

Foreword

  1. Aim of This Textbook
  2. Prerequisites
  3. Preface

Chapter 1: DC Circuits

  1. Charge and Coulomb's Law Development stage: 75% (as of June 12, 2005)
  2. Voltage, Current, and Power Development stage: 75% (as of May 2009)
  3. Basic Concepts Development stage: 25% (as of June 12, 2005)
  4. Cells Development stage: 25% (as of June 12, 2005)
  5. Resistors Development stage: 100% (as of June 12, 2005)
  6. Capacitors Development stage: 75% (as of June 18, 2005)
  7. Inductors Development stage: 75% (as of June 18, 2005)
  8. Other Components Development stage: 50% (as of June 12, 2005)
  9. DC Voltage and Current Laws Development stage: 50% (as of June 12, 2005)
  10. Nodal Analysis Development stage: 25% (as of June 12, 2005)
  11. Mesh Analysis Development stage: 25% (as of June 12, 2005)
  12. Thevenin and Norton Equivalent Circuits Development stage: 50% (as of June 12, 2005)
  13. Superposition Development stage: 50% (as of June 18, 2005)
  14. Diagnostic Equipment Development stage: 25% (as of June 12, 2005)
  15. DC Circuit Analysis Development stage: 25% (as of June 12, 2005)
  16. Measuring Instruments Development stage: 25% (as of June 12, 2005)
  17. Noise in electronic circuits Development stage: 00% (as of June 12, 2005)

Chapter 2: AC Circuits

  1. AC Circuits Development stage: 25% (as of June 12, 2005)
  2. Phasors Development stage: 25% (as of June 12, 2005)
  3. Impedance Development stage: 25% (as of June 12, 2005)
  4. Steady State Development stage: 25% (as of June 12, 2005)

Chapter 3: Transient Analysis

  1. RC Circuits Development stage: 50% (as of June 12, 2005)
  2. RL Circuits Development stage: 00% (as of )
  3. LC Circuits Development stage: 00% (as of )
  4. RCL Circuits Development stage: 50% (as of June 12, 2005)

Chapter 4: Analog Circuits

  1. Analog Circuits Development stage: 00% (as of June 12, 2005)
  2. Vacuum Tubes Development stage: 25% (as of June 12, 2005)
  3. Diodes Development stage: 50% (as of June 12, 2005)
  4. Transistors Development stage: 50% (as of June 12, 2005)
  5. Amplifiers Development stage: 50% (as of June 12, 2005)
  6. Operational amplifiers Development stage: 50% (as of June 12, 2005)
  7. Analog multipliers Development stage: 50% (as of July 19, 2006)

Chapter 5: Digital Circuits

  1. Digital Circuits
  2. Boolean Algebra
  3. TTL
  4. CMOS
  5. Integrated Circuits

Elements of Digital Circuits

  1. Transistors
  2. Basic gates
  3. Latches and Flip Flops
  4. Counters
  5. Adders
  6. Decoders and Encoders
  7. Multiplexers

Computer Architecture

  1. RAM and ROM
  2. Registers
  3. ALU
  4. Control Unit
  5. I/O
  6. RTN

Analog-to-Digital and Digital-to-Analog Converters

  1. Analog to Digital Converters
  2. Sequential Approximation Registers
  3. Digital to Analog Converters

Radio engineering

  1. Frequency Spectrum
  2. Gallery of VLF-signals
  3. VLF-reception with the PC
  4. Reception of DRM-transmitters
  5. Transmitter design

Appendix

  1. Definitions Development stage: 50% (as of June 12, 2005)
  2. Formulas
  3. Circuit Symbols (Editors should also look at Template)
  4. Identifying Components and Values25%.png
  5. Laplace Transform pairs25%.png
  6. Design Basics: Tools and Equipment
  7. Electro-Mechanical Analogies
  8. Expanded Edition

Resources: (When adding links make sure to fill out the Permission Form)

  1. Discuss this book
  2. GCSE Science/Electricity
  3. Wikipedia's Electronics
  4. Wikipedia's List of electronics topics


Resources that are not yet covered by the Permission Form

  1. Tony R. Kuphaldt's Lessons in Electric Circuits
  2. American Home Electronics
  3. An eBook resource site with related topics to RF, DSP and Electronics

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