Fox Valley Technical College Appleton, WI Communication Signals Voltage, Current, Resistance 10/1/20151

Electricity Where does it come from? 10/1/20152 Electric Charge What is it?

Foundation Regardless of the state or form that matter takes, it can be categorized into two groups. One group is the element, which may be divided yet maintain all of its characteristics until only one atom is present (like copper). The other group is the compound, which may be divided yet maintain its characteristics until only one molecule is present (like water). 10/1/20153

The Atom An atom is an extremely small particle invisible to the naked eye. The word atom comes from the Greek atomos, meaning indivisible. Only in recent times has sophisticated equipment allowed scientists to see atoms and prove their structure and existence. The characteristics of an atom or element is determined by the number of protons and neutrons found in its center or nucleus. 10/1/20154

Construction of the Atom Neutron Proton Electron Nucleus “Shell” Electrons are orbiting the nucleus at a similar distance from the nucleus, at an energy level called a shell. Each shell has a limited capacity for electrons. Additional electrons go into a higher energy level shell, further from the nucleus. The nth shell may contain up to 2n 2 electrons. 10/1/20155

Copper Atom ShellElectrons 12 (Full Shell) 28 (Full Shell) 318 (Full Shell) 41 (of 32 possible) “Valence Shell” = the outermost shell /1/20156

Atoms Classification for Electrical Materials: Conductors –1 to 3 valence electrons Semiconductors –4 valence electrons Insulators –More than 4 valence electrons 10/1/20157

Electric Charges Exert Force (Electric Force Field or Electromotive Force – EMF - it is measured in Volts) NO Charge  NO force Opposite Charges  Force of Attraction Like Charges  Force of Repulsion –– ++ +– –– ++ +– 10/1/20158

A Stronger Electric Force Field –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– More charges  Greater force  More Voltage 10/1/20159

Measuring Charge Two types: Positive and Negative (random definitions) Name for Unit of Measure: “Coulomb” Electrons in one Coulomb of negative charge: = 6.25 x electrons [by definition] (6,250,000,000,000,000,000) Charge on one electron: = –1.6 x Coulombs ( ) 10/1/201510

Net Positive Charge of an Atom When missing one valence electron, the copper atom has a net Positive charge. Then the copper atom has a force of attraction to another electron. +29 – 28 = /1/201511

Net Negative Charge of an Atom When having an extra valence electron, the copper atom has a net Negative charge. Then the copper atom has a force of repulsion toward the extra electron. +29 – 30 = /1/201512

Voltage 10/1/201513

A measure of the force that makes charges move Sometimes called “potential” Also called “Electromotive Force” or “EMF” Symbol: V Unit of Measure: Volt Can be stored like air in a balloon Voltage 10/1/201514

General Definition: The amount of energy per unit of charge required to move a quantity of charge between two points. Voltage One volt of electric field force is required when expending one joule of energy in the process of moving one Coulomb of charge from one point to another. 10/1/201515

10/1/ − −− −−− −−−− −−−−− Held in position Movable One Coulomb Electric Field Force Of One Volt One joule of energy is expended in moving one coulomb of charge from its initial to its final position.

Voltage Sources Regenerative Voltage Sources: Chemical: Batteries –(Rated in Amp-Hours of life) Mechanical: Generators –(Rated in kilowatts) Photo-voltaic: Solar Cells –(On a bright, sunny day, the sun provides approximately 1,000 watts of energy per square meter) Converters: Electronic Power Supplies –Convert AC to DC voltage and current 10/1/ Non-Regenerative Sources: Capacitors –Their voltage declines with use.

Cells and Batteries A battery is used to convert chemical energy into electricity. Sometimes, a flashlight cell is incorrectly referred to as a battery. A cell is a single voltage producing unit, whereas the battery is a group of cells that are connected so the output can be maximized. An automobile battery is made up of six individual cells resulting in a total output of 12.6 volts. 10/1/201518

Voltage Sources - Cell Electrolytic Chemical Positive Electrode Negative Electrode Battery Constructed of multiple Cells (Anode) (Cathode) 10/1/201519

Voltage Sources - Batteries Battery operation: Chemical interaction between the electrolyte and the electrodes. –Causes a continuous supply of electrons at the negative electrode. –Causes a shortage of electrons at the positive electrode. Eventually, the chemicals are depleted. –In some batteries, the chemical action can be reversed, “recharging” the battery. 10/1/201520

Two types of Chemical Cells Primary Cells –An alkaline cell is a primary cell which destroys itself in the process of creating an EMF. –Zinc-carbon, alkaline, mercury, silver oxide and lithium are examples of primary cells. Secondary Cells –found in the auto battery (lead acid) or the nicad cell found in many portable telephones, are rechargeable and my be reused many times. 10/1/201521

Voltage Sources - Batteries + – + – + – + – The voltages or potentials add. The current capability is the same as one battery. Batteries connected in SERIES 10/1/201522

Voltage Sources - Batteries + – + – + – + – The voltage or potential is the same as one battery. The current capabilities add. Batteries connected in PARALLEL 10/1/201523

Voltage Sources Solar (Photovoltaic) Cells Made of semiconductor materials. Doped silicon is the most commonly used material. When light strikes the material, a portion of the light is absorbed, imparting energy to valence shell electrons and allowing them to move more freely. The light also produces electric fields that induce electrons freed by light absorption to move in one direction. It's only fuel requirement is light and it leaves no pollution. Solar energy is used to power most satellites that orbit the earth. 10/1/201524

Current 10/1/201525

Current The continuous movement of charge over time The rate of flow of charge Symbol: I Unit of Measure: Ampere 10/1/201526

Current General Definition: The number of charges flowing through a cross sectional area per unit of time. 10/1/ One ampere flows when one Coulomb of charge moves through a given cross- sectional area in one second.

Current Without voltage applied, free electrons in a conductor or semiconductor move at random. 10/1/201528

Current Free electrons under pressure to move. 10/1/201529

Current 10/1/ As each electron vacates a valence shell, it leaves a hole that can be filled by another moving electron. If electrons are forced to flow in one direction, their vacated holes appear to flow in the opposite direction. Hole Electron

Current - Rate of Flow Unit: One ampere flows when one Coulomb of charge moves through a cross-sectional area in one second. 10/1/201531

Current Hole Flow (+ to -) (“Conventional” Flow) Electron Flow (- to +) 10/1/201532

Voltage - Current Convention Voltage - Current Convention Conventional Current Flow I +V−+V− Passive ComponentsVoltage Sources I VSVS 10/1/201533

Voltage - Current Convention Electron Current Flow I +V−+V− Passive ComponentsVoltage Sources I VSVS 10/1/201534

Resistance 10/1/201535

Resistance A measure of the opposition to current flow in a given material. Symbol: R Unit of Measure: Ohms 10/1/201536

Resistance Definition: The property of different materials to restrict electron flow differently. 10/1/ One ohm (Ω) of resistance occurs when one volt of potential is applied and one ampere of current flows.

Resistor Symbol 10/1/201538

Copper wire resistance table AWGFeet/OhmOhms/100ftAmpacity *

Resistance vs. Impedance We use two different words to describe the fact that a given material or device will let electrons flow just so fast at a given voltage: We reserve the term “Resistance” for purely resistive components used in DC and AC circuits. We reserve the term “Impedance” for other types of components in AC circuits. Impedance is a topic reserved for more advanced studies in electronics. 10/1/201540