ELECTRICITY

Learning Objectives Characterize voltage as the force that causes electrons to move. Compare the characteristics of AC, DC and Static Electricity Compare the methods of creating voltage in AC, DC and Static Electric systems. Compare methods of storing electrical energy. Classify materials as electrical conductors or insulators. Explain amperage as the measurement of electric current. Relate electrical resistance to the characteristics of a material. Define an electric circuit as a system that uses electrical energy.

What is electricity? The movement of electrons down a concentration gradient, through a conducting material, in such a way that the kinetic energy of the electrons can be turned into some other form of work or energy. – Requires a significant difference in concentration of electrons – Requires a system to conduct the electrons and convert their energy into something useful (Electric Circuit) The work done by the electrons depends on: – The concentration difference – How many electrons are moving at one time

Types of Electricity Static Electricity – High concentration of electrons build up in an area compared to surroundings – When two areas with different electron concentrations come together electrons move from high concentration to low concentration (spark) Alternating Current (AC) - House Current – Produced by rotating a wire loop through a magnetic field – Electrons vibrate back and forth in place without travelling through the circuit Direct Current (DC) - Battery Current – Produced by processes that produce electrons in one area and use electrons somewhere else – Electrons don’t move unless two complimentary regions are connected

Static Electricity Some physical processes cause electrical charges to concentrate in different locations separated by a material resistant to electron movement. The separation of charge builds up an electrical field. As field strength increases it finally overcomes the resistance and a spark is produced. – A spark is actually a micro-thin filament of super heated (plasma) air produced as electrons jump through air. Causes: – Rubbing feet/shoes on carpet can produce up to about 1000V – Movement of charged particles in clouds can produce voltages upwards of 100,000,000V creating lightning.

DC Voltage Systems Direct Current (DC) - Electrons flow in one direction from negative to positive regions of voltage source. – Each electron travels the entire electrical circuit. – Direction of flow is always negative to positive – Most commonly produced in battery systems

Batteries & How They Work How They Work – Use chemical reactions, one that needs electrons (positive) and one that produces electrons (negative) – The reactions can’t work until they are hooked together – When connected, the electrons flow from where they are produced (negative terminal) to where they are needed (positive terminal) – When the reactants in either reaction are all used up the battery no longer produces voltage (dead battery) – In some batteries the reactions can be reversed and the batteries “recharged” and reused (NiCad, NiMH, Lithium Ion, Lead Acid). – Battery chargers force electrons to flow in reverse direction (positive to negative), forcing the chemical reactions to go in the opposite direction regenerating the original reactants – Different battery types use different chemical reactions, producing different voltages

Multiple Battery Systems Hooked in Series – Multiple batteries (of the same voltage) can be hooked together head to tail (+ to -) to increase their voltage output – Voltages add together to get total system voltage 2 – 12V batteries produce 24V – Combining batteries of different voltages will destroy the lower voltage batteries Hooked in Parallel – Multiple batteries can be hooked head to head and tail to tail to increase the number of electrons available to move at one time – System voltage is the same as individual voltages 2 – 12V batteries produce 12V – Increased time of electrical output before batteries go dead – Increase number of electrons available to flow at one time

AC Voltage Systems Alternating Current (AC) - Voltage is produced by a wire loop rotating in magnetic fields. – As the wire is passed through one field, the electrons flow in one direction, as it passes through the next field the polarity is reversed and the electrons flow in the opposite direction. – Direction of movement changes 120 times / second (60 cycles) – Individual electrons stay in one region of the circuit and vibrate back and forth. – Most AC current produced in power plants by huge generators, then shipped through transmission lines (electric grid) –

Measuring Voltage in an Electrical System Voltage is the force in an electrical system that makes electrons move. To measure voltage you need to know the difference in charge between two regions. To determine the voltage of a system, or regions in a system, use a voltmeter. – Voltmeter – Electrical device that measures voltage difference between any two points – Can be used to measure AC or DC electricity – Connect + and – leads to any two points and the meter will register the difference in voltage between the two points. Remember: The higher the voltage is between two regions, the more likely electrons are to move between the two regions and the more work the electrons can do as they move.

Electrical Current Electrical current is the rate of flow of electrons in an electrical system. – The standard unit of current is the Ampere (amp) – 1 Amp = 1 Coulomb of charge moving past a point in 1 second Electrical current is measured with an ammeter 2 types of ammeters – In-line - Hooked into electrical circuit so that current runs through it – Clamp on - Clamps around the conduit current is running through Voltage burns, Amperage kills! – Voltage will cause electrical sparks to jump from one place to another, superheating the air and may burn skin if the voltage is very high – Amperage is the flow of electrons and even small amperage currents can interfere with the electrical activity of the heart, muscles and nerves

Alternating Current - Frequency & Period In direct current (DC) electricity the electrons travel from the negative terminal to the positive terminal In alternating current (AC) electricity the electrons vibrate back and forth in the same place – The speed of the vibration is measured in cycles per second (hertz) – The time for one complete vibration cycle to occur is the period – Formula:F = 1/PP = 1/F – AC current in the United States has a frequency of 60Hz (60 cycles per second)

Material Classification Electrical Conductors – Carry current with very little resistance (friction) – All are conductive metals – Best Metal Conductors Gold, Copper, Aluminum, Silver Superconductors – Composite ceramic materials with 0 resistance at low temps – Made with rare earth metals such as Yttrium Insulators – Materials that are resist the flow of electrons – Non-metals Semi-conductors – Conduct electricity under certain conditions or in 1 direction

What is Electrical Resistance Electrical resistance is the friction electrons encounter as they move through a conductor. – For most circuits major resistance is encountered where the electricity is turned into some other form of energy – Resistance depends on: Material the conductor is made of Number of electrons being moved at any one time (current) Force that is causing the electrons to move (voltage difference) Unit: Ohm (  ) – 1 Ohm is the resistance against which 1 volt of charge difference will transport one coulomb of charge in 1 second.

Basic Electric Circuits Basic electrical circuits are composed of 4 major parts. – Voltage Source - There has to be a voltage difference present to make electrons move Batteries or capacitors can produce Direct Current Alternators and generators produce Alternating Current Several batteries may be hooked together to increase the Voltage – Conductor - There has to be a connection (usually wire) between the high charge and low charge areas of the circuit Gold, Silver, Copper and Aluminum are the most common conducting materials used in electrical circuits – Switch - Working circuits must have a switch to turn the circuit on and off On/off switch Breaker or Fuse – Load - Light, motor, or other electrical appliance that turns electrical energy into some other form of energy There may be several loads in a single circuit

Electric Circuit Diagrams Voltage Source - Parallel short & long lines – Positive side - long; negative - short – Electricity always flows negative to positive Loads - Zig zag line - electrical appliance or light bulb – Loads are the locations where electrons actually do work – Loads often convert electricity to different forms of energy or work. – Loads produce resistance to electrical movement Switch - Arrow or line between 2 dots – May be closed (straight) or open (tilted up) Conducting Wire - Thin lines connecting other components