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DMI 50B ELECTRICITY Kyle Thornton

Why Study Electricity? Electric energy is supplied to the x-ray tube in order for it to function The x-ray tube converts electric energy into x- rays This is the primary function of the x-ray unit

Electrical charge Electron - smallest unit of electric charge A mobile charge carrier Can move from one point to another Carries a negative charge Proton - Equal in mass and weight to electron Bound in the nucleus Carries a positive charge

Terminology Neutral object has equal number of protons and electrons Ion pair Electron removed from atom Atom becomes a positive ion More positive charges Positive atom + free electron = ion pair Radiation passing through matter causes ion pairs - potentially harmful Ground A conduit for excess electric charges to move through

Divisions Of Matter Insulator Does not allow an electrical charge to move freely Conductor Allows a charge to move freely Either through it or on its surface Semiconductor A charge moves through easier than an insulator but not as easy as a conductor

Electrostatics And Electrification Electrostatics Non-moving electrical charges Static electricity Electrification Removal or addition of electrons An excess or deficiency of electrons will determine if positive or negative

Methods Of Electrification Friction Removal of electrons from one object to another Usually by rubbing the objects together Simplest form of electrification Contact A body charged by friction touches another object Confers the same type of charge

More Methods Of Electrification Induction All charged objects have an electric field Uncharged metallic object will experience an electron shift if brought into an electric field Only the electrons move

Laws Of Electrostatics 1.Like charges repel; opposites attract 2.Electrostatic force - Coulomb’s law Inversely proportional to square of the distance between two charged objects 3.Electric charges reside only on the surface of conductors 4.Concentration of charges on curved surface is greater where curvature is greatest 5.Only negative charges can move in solid conductors

Electrodynamics Charges in motion Current - Flow of charged particles 1. In a vacuum 2.In a gas 3.In an ionic solution 4.In a metallic conductor Current is measured in amperes - A

Sources of Current Cells or batteries Converts chemical to electrical energy Dynamo or generator Mechanical to electrical energy Solar Atomic Wind Geothermal

How does electric current flow? There must be a path on which to flow Circuit Generally controlled by switches that open or close the circuit There must be a potential difference between two points within the path Voltage or V This is usually supplied by a battery, power supply, or electrical outlet

Resistance Acts to oppose current flow Resistance is generally present in all materials Resistance is measured in Ohm’s or Ω Resistance is determined by: The material of the conductor The length of the conductor The cross-section of the conductor

More on Resistance icity/resistance.html#CODE icity/resistance.html#CODE

Ohm’s Law The relationship of current, voltage, and resistance in a circuit If voltage is increased, and electrons are available, the electrons will move faster Current flow is affected by resistance Resisitors may be added to the circuit to regulate and direct the current flowing through the circuit file:///C:/DOCUME~1/kthornto/LOCALS~1/Temp/phe t-ohms-law/ohms-law_en.html file:///C:/DOCUME~1/kthornto/LOCALS~1/Temp/phe t-ohms-law/ohms-law_en.html

Ohm’s Law, Continued Voltage = Current X Resistance or V = I X R or R = V/I or I = V/R

Work The Following Problem A 1.5 battery produces 300 mA. Determine the resistance of the circuit. Given: V = 1.5 I = 300 mA = 0.3 A R = ? Ohm’s law = V = IR or R = V/I Answer: 1.5/0.3 = 5 ohms

Types Of Circuits Series All resistors are connected in a continuous line If a resistor is damaged so that current cannot flow, it won’t flow through the entire circuit

Types of Circuits Parallel All resistors are connected side by side If one resistor is broken, there is still a path on which to flow

Ohm’s Law In A Series Circuit Rule #1 I(T) = I(1) = I(2) = I(3) The current in each circuit component is constant Rule #2 V(T) = V(1) + V(2) + V(3) The total voltage is equal to the sum of the voltage in each component Rule #3 R(T) = R(1) + R(2) + R(3) The total resistance is equal to the sum of the resistance in each component

Ohm’s Law Website ohmslaw/index.html ohmslaw/index.html

More Practice With Ohm’s Law There are three resistors in a circuit. They have the following magnitudes R(1) = 8, R(2) = 10, R(3) = 6 What is the total resistance? Answer = = 24 Voltage = 12 Find the total current. Current = V/R Answer = Amperes = 12/24 = 0.5 A

Ohm’s Law In A Parallel Circuit Rule #1 V(T) = V(1) = V(2) = V(3) Rule #2 I(T) = I(1) + I(2) + I(3) Rule #3 1/R(T) = 1/R(1) + 1/R(2) + 1/R(3) The total resistance is inversely proportional to the sum of the reciprocals of each individual resistor

Total Resistance In A Parallel Circuit R(T) will always be less than the lowest individual resistance in the circuit Find the total resistance for the following: R(1) = 4, R(2) = 3, R(3) = 12 1/4 + 1/3 + 1/12 3/12 + 4/12 + 1/12 = 8/12 R(T) = 12/8 = 1.5 ohms

Series and Parallel Circuit Diagram ed.org/EducationResources/HighSchool/Elect ricity/seriescircuit.htm ed.org/EducationResources/HighSchool/Elect ricity/seriescircuit.htm

Charge Flow Direction: Direct Current vs. Alternating Current Direct current - charges move in only one direction The type that is supplied by a battery or DC power supply Alternating current Alternates its direction of motion It flows one direction during the first half Reverses direction in the second half Divided into cycles 60 cycles per second in the US One full cycle is 1/60 second One half cycle is 1/120 second There are 60 cycles/second This is called a 60 Hertz AC

Examples of DC and AC feature/acdc.html feature/acdc.html ed.org/EducationResources/HighSchool/Electrici ty/directcurrent.htm ed.org/EducationResources/HighSchool/Electrici ty/directcurrent.htm eg&feature=player_detailpage#t=8s eg&feature=player_detailpage#t=8s k&feature=related k&feature=related

Other Circuit Components Capacitor A device that stores electrical charge until needed Generally consists of two metal plates dex.html dex.html Rheostat A device to vary resistance Produces gradual changes in voltage or current flow nce/index.html nce/index.html

Electrical Power Measured in Watts Watts = Volts X Amperes